For all of the young people watching this, try to imagine growing up in the 70's and 80's, being 15 or 16 years old and trying to figure out this stuff before the internet and smart phones. My current carb (Since 2006) is a 1095CFM Demon. My cousin, (A younger, LS guy) refers to it as "A semi controlled fuel leak". Fuel injection is awesome, carbs are old school, I enjoy them both.
it was hard at the time to learn how to work on carburetors... now imagine a young guy choosing carburetor over efi and making more power! that's me. one of my close friends, a remaper, believed that carbs are worthless and not reliable to tune up to make power until he bought a peugeot 205 tu3 with weber carb on it, as he tested the car to see AFR with wideband sensor he have seen the most stable AFR ever on the whole rpm range of the engine, excat 13.5 to 1! he has quit making jokes out of my car since then. i drive a peugeot 405, hand made engine (xu7 internal - xu5 cylinder head - xu9 camshaft - lightweigh flywheel and pulleys), 10:1 CR, 1800cc, aisan 2f carb, fantex delco and coil, magneti marelli ignition module. my next project is to remove camshaft mechanical fuel pump and add high pressure/flow hearting pump.
Efi makes more power lower rpm, but the carburetor makes more in the higher rpms. Naturally aspirated, of course. There's many dyno videos that prove it. Younger tuners seem to hate it but numbers are numbers
Think about what it was like before you could buy off the shelf camshafts? My Dad used to grind his own back in the day (early 1960's) because there was no "performance store" available, you were it! there was know "knowledge base" to reference on profiles, ramp up, durations, degrees. You started with a piece of 2.5 bar stock!
At 65 I regret not seeing this invaluable information using the guessing game is not really fun. When I had it close, things would make me change my guesses, and then lose track of where I had just left off. Thanks for the encouragement!
I bought a new 600 cfm Holley from a guy that said he couldnt get it to run correct. I put it my vehicle and it did run rough. So i investigated and found out that the accelerator linkage cam was set incorrectly. Reset it and it preformed great.
I have a feeling that a carb tuned by you would be just as good as a Holley sniper unit without worrying about electronics leaving you on the side of the road, keep the videos coming
@@patrickharper9297 why would you change Jets regularly? Unless you modify the car once you get it jetted right its done. The worst I've ever had to do is just adjust the mixture screws at idle when the weather changes or I do a tune up.
I remember the days long before AFR gauge availability... the way to tune any carburetor was to read the spark plugs, the use of a vacuum guage, seat of the pants feel(butt dyno) and to get a better handle on tuning for max power, was to take your car to the 1/4 mile track and adjust accordingly.
Most people problem was their ears & butt dyno got very comfused once the time clocks popped up! They always thought the bigger the cam sounded the faster it was! And it would be ok as long as it was blowing the tires off!
Ford carbs used the same valves on 2 barrel and 4 barrel flat top carbs in the 60s and 70s. Worked on a lot of them. Ford called it an economists valve. Found below the float bowl. Turn the carb over and under a cover held on with 4 screws holding the cover.
Inspection plugs in the exhaust... and chaining the front down and putting it in gear accelerating in a pull to set the timing.... Crazy as you may,,, it works.😜 I always loved a Quadrajet ....but it's what I knew but once I started messing Holley I was impressed....Fuel injection is much more Simple.... once you learn... After all my rambling..... Very informative Video content... thanks
I remember the 67 Chevy Caprice with the Big block 427 had a factory vacuum gauge and there was others in a long them year's also had factory vacuum gauges....A crucial measurement.. I also installed inserts in the manifold and or Header's back in the day to read the color of the exhaust Flame..... other little tricks putting the car under load while setting timing and there are many other recurve Kit's and on and on..... Very good content here😎
Holley used to recommend a different process for PV. **Automatic timing & idle set, engine operating temp, “In Gear”: Vacuum hg minus 2hg= base PV. **Manual transmission timing & idle set, operating temperature: Vacuum hg divided by 2= PV.
I'll just correct one thing you said at around 5.30 ...you mentioned the vacuum hits the diaphragm which overcomes the spring letting fuel to pass...actually the other way around...vacuum holds the valve closed then when vacuum drops under load the spring opens the valve allowing fuel to flow...when vacuum recovers it overcomes the spring and closes the valve again. I'm guessing that was what you might have meant?
One needs to realize that the idle mixture (AFR) will be unaffected by whether the PV is open or closed. This is because the fuel admitted from the PV feeds into the PVCRs at bottom of the main fuel wells; at idle, the main circuit has not started as evidenced by the fact that there should be no fuel flowing from the boosters. When the PV should open is when the engine load increases decreasing the engine vacuum such as going up an ever-increasingly steep hill or opening the throttle under load. In other words, the PV should open when the mixture starts to become lean (or 2" Hg vacuum prior to this point) under load to enrichen the mixture. Although the guidance of "idle vacuum divided by 2" may work in many cases, it is better to establish when the mixture starts to go lean and then add 2" to this point to select which PV to use.
I like your info. Makes sense to me. But when do you know when you’re 2” hg before lean condition? The air fuel ratio and vacuum reading will change rapidly at say, a launch at a drag strip. How do you determine the point to choose the valve?
Ohhhhh, yes! Thank you for another great and informative vid. It seems like the power valve is often overlooked. Great tips, especially with the right size carb. Be it car, truck or motorcycle, you're right, it's often a setup with a carb that is too big. Thanks!
I was surprised you didnt go over how the early holleys didnt have power valve savers and when the engine backfired it would blow the power valve diaphragm out and it would just mess up everything. I used to drill out the power valve channel and install check valves but holley does that now..!! Lots of good info ...!!
Time. Time dictates everything. If I include too much information, folks seem to get spicy about it. So I try to compact it all in and not go down every possible rabbit hole on a topic. That’s difficult to do sometimes! Thankfully Holley fixed that issue in the 90s cuz back in the day… we changed a LOT of blown power valves. 😂
This is good general information it would be good to pinpoint some common scenarios on Holley carburetors. The problem I found with most Holly's is cruising down the road they are usually too rich like 11 to 1 but under wide open throttle they are very close 12.8 to maybe 1 3. To get that cruising air fuel ratio 14 to 1 and then have a good tip in plus wide open and then idling is very difficult to achieve
Would love to include everything in one video but 20-25 minutes seems to be the tipping point. Any longer than that and people just don’t watch. Or they complain nonstop that the video was too long. 😆 I have more planned. We’ll eventually cover everything.
I have found most guys put larger front jets in to get rid of the lean stumble that occurs while cruising and trying to gain a few mph. They should’ve corrected the stumble with a power valve as described in this video. The issue is with the words Holley uses when you’re using their Hot Line because they say the Power Valve is a power adder. This wording plays with your head because, okay yeah it adds extra fuel just before the lean stumble occurs adding power to gain or maintain the speed you’re cruising at. So the guys only want it to quit stumbling when they’re out cruising and already have the great track times, so now they jet up the front jets like Holley tells them making the cruise mixture rich and then when you go WOT everything is great. If you adjust the cruise mixture using an O2 sensor you end up putting the original jets back in and sometimes one size larger (due to the ethanol added in the fuel) and then make the driveability correction with a power valve that opens just before the lean stumble occurs. You want the power valve to open at least one inch of vacuum higher than the stumble occurs.Have someone watch the vacuum gauge and when the needle suddenly drops to 0” say at 7.5”. Install a 85 Power Valve.
Hi! I am a new subscriber. I am very new to this and found out I know nothing! Lol! I am going to lean as much as I can. Thank you for sharing the knowledge
They were known as economy valves many years ago. Two stage power valves were great. The problem is that most people did know anything about power valves to begin with. This valve was for those who understood on how to use them.
Biggest problem with holly carbs is people tune them completely wrong. They have a reputation for being thirsty and not good for the street. The main jets control the cruise mixture, and the PVRCs control the WOT mixture. Sure in a race application go ahead and block the power valves off and set the WOT mixture with the main jets. As for a street application no matter if it’s a 200 HP bone stock 6 cylinder or a 1000 hp monster you NEED metering blocks with replaceable PVCRs, air bleeds, idle jets, and emulation tube jets. A 4150 or 4500 holly can be tuned to give great results throughout the RPM range and at different throttle openings. Jet the carb for the leanest possible cruise mixture that allows smooth engine operation with the main jets. Then jet it for max power with the PVCR jets. Granted tuning a holly style carb is a bigger pain in the ass then a Weber or Carter style carb because you have to pull the bowls, metering blocks and power valves to make adjustments, however they can be tuned to deliver the same air fuel ratios under the same conditions. Your best bet is to try and find a set of those wonderful metering blocks for the 4150 that take Weber calibration parts! Those blocks were wonderful because you could tune the carbs as easily as a downdraft Weber including changing jets without even shutting down the engine! No idea why they stopped making them but If you can find a set grab them!
Great video best one out there easy enough to try two different ones if you don't have AF readings then you find what it likes depend on camshaft overlap selection bottom line more cam less vacuum
All good information.... of course we have more questions. With a Manual transmission, the vacuum varies. Add in a draw through turbo setup, and im scratching my head as usual. I see a rich condition under load for sure...and sometimes a lean condition depending on gear im in at the time. and cant seem to jet it down (or up) far enough to fix this. The power valve is my next direction. I assume you will see the power valve open on your AFR gauge. I need to pay more attention to this. Thanks for the tips
Not sure we’ll get there anytime soon. Though I am itching to get back into another drag car. With the drag and drive events so popular now, that might be on the list to build some day soon.
I use a air fuel meter and vacuum gage to tune mine. Main jets for air fuel ratio of 14-1 at 2500 driving down the road and the power valve vacuum setting for when it leans out. Right now running 69 jets and 2 inch power valve on a 500 cfm 2 barrel .
From my understanding and studies, the purpose of the power valve is that it allows you to cruise (pretty much at any speed) and you want it to remain closed. You only want to open the flow and enrich when under larger power demands like spirited acceleration and/or WOT. PV's allow the carb to downsize the main jet about 7 numbers vs no power valve so that you can cruise and sip fuel. So where I get a little lost in this video is the various cruise tests. I would be reading those vacuum readings and making sure I chose a PV which is closed under all of those cruise conditions. I am learning all I can and working hard trying to tune multiple holleys to get one working well on my hot 327SBC, but I can't say I'm doing so well yet. Using vacuum, wideband, tach, and video recording gauges and trying..... Have a horrible lean condition on throttle tip in.
Speed is the easiest way to help understand opening events and driving data. It’s easy because we can work with something everyone can measure like MPH. Load, no so much. Looking at this I could have done a better job of explaining the why. If I could, I’d just have everyone run a data logger and we can see the full run and when those lean/rich condition occur. For sure when we start doing tuning videos on both my truck and Chevelle, we’ll walk through the process with more clarity. Thanks for the note. Very helpful.
One of the things that make a huge difference is in gearing. My car no overdrive with 3.25 gears high stall you cant lug it. Hard to get vacuum to drop much during normal driving. Now put an overdrive it, a heavy car with a lockup torque convertor and every hill you go up vacuum will drop a lot. I try to size the vacuum opening for normal driving so it stays closed. But I'm trying to run around 14-15 fuel ratio. If it pings due to lean or advance timing you could cover it by opening the power valve just before the ping. Great video. I do have a data logger.
I would go with annular boosters instead of straight or dog leg boosters. The lean tip in at cruise speed is either the transition circuit going lean before booster take over or insensitive boosters not activating soon enough. Carb size problems are really just booster and emulsion problems.
Looking forward to your reports about tuning the edelbrock 4150. I will tune right along with you since I have my own edelbrock 4150 that I will try out on my current engine build. And I have a lot to learn.
Very cool! Thank you. For sure we’ll be tuning the 650 on my GMC and later on when the big block is done on the Chevelle we’ll be tuning an 850 on it. Lots to cover between now and then! I’ll be doing more content on the 4150 series carbs very soon.
There is no such thing as a carburetor that is too large. The emulsion well is the least understood area of ALL carbs, not just holley's. You described power valve operation precisely backwards. Engine vacuum keeps the valve CLOSED, not open. The power valve channel restrictor under the valve should be used to tune WOT operation and the main jets used to tune cruising A/F ratio.
I disagree, if the carb is capable of more air than the engine will ever need or use then its too big. You can argue that a 4 cyl can run with a 1000 cfm carb which is true but nobody sane thinks it would run well.
@@cuzz63 not within the context of the video. Just putting a high capacity carb on a tiny engine was not the discussion. Design of the carb circiuts was and a carb of the correct design would work well. However using just any carb would not work well. Most carbs are chosen using the wrong criteria as in it's rated flow rate instead of the booster design and fuel curve needed. Most dyno tests for carbs are really booster tests. For example, an I R type system with 300 CFM per carb will make more low speed torque than a small 4 barrel on a 302 cu inch v8. Why? Because the flow rate isn't the issue, the atomization of the fuel due to internal design is.
This is an interesting discussion. I've done my share of Holley carb tuning rebuilding over the years. 100's of them. If I take a Holley plug the power valve, a part is specifically made for this, I will get better gas mileage. I see no noticeable difference in performance. But then, I'm not massing the throttle to the floor but driving normal. So the only thing I infer is the power valve still dumps fuel even under no load.
Im confused on your manifold vacuum theory. To my understanding manifold vacuum decreases the more open the throttle is. That would make the valve function the opposite way that you explained it.
Hello, good video, very good explanation, you touched on a topic where you mention a carburetor with very high cfm for a very small engine. I will be waiting when you explain the physical difference from an 850 cfm to 650 cfm for the street and how to try to correct it. Thank you.
I fought the concept of fuel injection about as hard as I fought the concept of buying CD's instead of vinyl records, but with fuel injection, I didn't have all the trial and error, test runs, driving conditions, and removing the float bowl assembly to get to the metering block and jets every time it needed adjustment. You just plug in the laptop and tell it where to add/remove fuel at a given load or RPM. I love the simplicity of carburetors, but the tuning takes skill and patience that most old school rodders don't bother with, and just settle for a close, off the shelf carb.
@@stephencarr7173 that’s very true. The trouble with carburetors is people get used to how bad it runs because it may start fine and maybe operate ok at WOT so they assume it’s good. They learn to put up with rich conditions, fouled plugs, contaminated oil, the garage stinking of fuel, burning your eyes out standing behind it at idle…every bad operation they just accept. It’s a carburetor, that’s the way they work. NO! It’s one of the reason why I started this channel. For gods sake tune that thing and realize it’s full potential! EFI is a whole other ballgame. Wait till I start doing more tuning videos on those. 😉
Too bad about the two stage power valve. I tuned my 650 DP using one. It allows a leaner cruise mixture for economy and the first stage takes the flat spot out when pulling hills and keeps the full metering block restrictions from opening. Better drivability, better control of the mixture. Std equip on an 85 GT 5.0L mustang. Not looking forward to the day it fails.
So help needed. I have a ATM Innovations XRSB-750. I'm running really rich 11.2 at idle and 14.0 at cruising speed. The fuel is pushing out of the exhaust at Idle and wanting to die upon any acceleration. For context I have pump nozzle of 31 primary and secondary 35 high speed bleeds 70 idle air bleeds .78 primary main jet and .93 secondary, 33 idle feed restriction, 2.5 power valve and 110v needle and seat. Timing locked out at 38 with 7.5 psi of fuel pressure that can be regulated down if needed. My question is what changes do i need to make to fix the off idle stumble/car completely dyeing or choaking out and the extremely rich low end. Thanks in Advance
This is very good. if you have a "fully" adjustable carb as the new Edelbrock 4150 or one like it and you have an dual ARF gauges (v8, 1 for left and 1 for right & dual plane manifold), vacuum gauge and a human data logger. How do you know what to change? power valve, PV restricter, high speed, low speed air bleeds, air bleed restrictor, etc. I get if AFR reads lean at X RPM I need to add fuel to a circuit that affect that RPM. I've read the Holley red book on 4150/4160 and David Vizard's Super Tune and Modify Holley Carbs book. I'm having trouble turning words and pictures into practice. I've probably read what I need to know and didn't realize it, so maybe hearing it another way would turn the light bulb on.
I’m going to do quite a few videos in this once the big block for the Chevelle is done. It’s an extremely long process and very very technical. But you’re spot on that a dual wideband O2 will be extremely helpful. Absorbing good tuning information online for sure will help. The good things is as long as you don’t go too lean, it’s something you can tweak on your own and learn as you go. Just take really good notes along the way. What your AFR readings were at the rpm you’re monitoring and what your changes were. That way you can always go back if you get too deep into the weeds.
If your engine is cammed up, don’t be surprised if you have to use a 105 Power Valve and install one size larger front jets than what came in the carburetor stock when using Premium gasoline that has the 15% ethanol.
Hey you put out some very informative videos. Just a question or two if you don't mind. What would the 30, 40, 50 and 60 MPH show me on my vacuum gauge and my wideband? I understand the vacuum will drop but at what steady speed should the PV kick in? Or am I misunderstood something? Maybe you could do a video (I'm sure it would help a lot of us) on exactly how and when the jets work, how and when the squirters kick in and for about how long. How and when the PV kicks in and when should the secondaries kick in on the jets and/or the PV. Or do the jets along with the PV on the secondary side kick in exactly at the same time? Sorry if I'm going overboard but that would explain a lot, especially to me.
the PV shouldn't kick in at any steady speed. it should kick in when you leave cruise mode and move to acceleration situation. i guess, what it was tried to explain, that if you monitor your engine in different steady speeds, then watch to which rating the vaccuum drops when you then want to accelerate and choose your PV near that point
Question? Am I correct is saying that if the rating of the Power Valve is lets say a 6.5 and that's higher than the idle vacuum at 5 inches of vacuum at 900rpm the engine will run too rich because the Power Valve is Open, and if the Power Valve is a 2.5 the engine could run lean until the engine vacuum is below 2.5 inches of vacuum? On this new build I have a new AED 750dp on a Chevy 302ci with 10.5 compression, Comp Cams custom grind solid flat tappet with .516 intake and .537 exh lift with 242 intake and 250 duration @ .050 and with a 110 lobe separation, valves set to .012 cold, new MSD ignition and pro-billet distributer, Victor Jr intake, AFR 180 Street Heads bolted to 1-5/8" headers to 3" flowmasters. It mated to a M21 trans and 3.90 gears on a 28" tall tire. I had the timing at 19* initial and 36* with the same problem but my Brother told me it was too much for 91 pump gas so I lowered it to 13* btdc initial at idle and 32* total. Plugs are all consistant light tan color as well. The problem I'm having is an intermittent lean pop and low power through the carburetor when under load accelerating in 1st gear under 3k rpm and inconsistent idle rpm when warm to operating temperature. I'm at 1-1/2 turns out on the Air/Fuel screws, accelerator pumps adjusted properly with cams in the #2 position. I just opened the secondary butterflies because too much of the idle slot was showing from the underside of the primary butterflies (this did help the idle but is lower idle at operating temperature than when warm). The standard squirters are 31's as well. The vacuum at 900 rpm is at 5 inches so I put a 2.5 power valve in it and didn't think about it much until I watched your videos on this subject. I'm thinking I should have a 4.5 power valve. Am I on to something here or what else can I check or adjust? BTW, above 4k rpm it's an ANIMAL for a 302! Thoughts?
Does any of the vacuum gauge tuning advice change for an airboat application since it is always in gear and under load due to the prop spinning at idle?
How do you adjust with 2 power valves? Do you run a smaller one on the primary and a bigger one on the secondary if its vacuum secondary or run them the same size?
I have a old 600cfm 4160 on a ford 289 and at half to full throttle it’s way rich idle is good but regardless of how much tuning I do I can’t get it to lean out at part and full throttle. It has a 6.5 power valve that came with the kit.
@@MuscleCarSolutions well I’ve been thinking about it. Warmed up it reads about 15 inches of mercury. It has a small cam in it. So I’ve been trying to figure out what size power valve I should get. And at those throttle positions, the AFR‘s bounce between 12 and 10.
Well at half throttle the PV should be open. So try a smaller PV and see if it leans that condition out. Try a 5.5 next and see how it does. If it gets better but not perfect, try a 4.5. Start with the 5.5 though. Make small steps. If that helps, then you’re on your way and retune. The 600 is probably too much carb, especially if that’s a mostly stock 289, so you’ll not get it perfect but you can make it better.
What is your opinion on a PV choice when the cam has a lot of overlap down low with low vacuum? Cruising speed has good vacuum tho. I get 8 to 9 inches of vac when in park and drops to 6 when in drive. I'll get over 12 at cruise.
@@FrankenVega always a bit of a moving target. AFR makes it easier but in absence of that, I’ll generally start with a numerically lower size and adjust up. Won’t take long to figure out when it’s supposed to hit and when it’s awful. I’d start with a 4.5 and move up from there.
throttle position and inches of vacuum [load ] tell u when the mixture occurs . An Air/fuel gauge tells u how much [quanity] fuel. Advanced tuning methods a vacuum gauge can do both
so when you are checking engine vacuum at 30, 40, 50 and 60 mph - do you take that number and use it for the power valve, or do you still divide it by 2? Thanks!
Ok. So. Suppose you have 9-10" of vacuum at idle and you go all the way up to a 8.5 power valve and you still have a tiny hesitation at around 9" are you supposed to go to a 10.5 p/v? Or play with cams and accelerator pump shots? At what point does that come into play?
If you're still responding to this video. It sounds like the higher the power valve number the sooner it opens?? Maybe it sounded like the lower the rpm the more vacuum so a higher rated power vacuum is needed. Something sounded backwards. I think where you said the engine will see 4.5 vac before it sees 3.5 is where I got confused.
Go and rewattch the video. 12:30 is what you are referring too. When you go WOT the vacuum drops down. If you have 8 inches of vacuum at idle, you divide that # in half, which would be 4. So your choice is a 3.5 or a 4.5 power valve, they don't make a 4.0 A 4.5 pv will allow fuel earlier than a 3.5 pv as the vacuum drops. If the carb is on the rich side, then I'd try the 3.5 pv which would help lean it out in that scenario.
Great vid as always, this may be a stupid question, but I've looked around a bit and haven't found a good answer. Power valve in secondaries, is there an advatage if so how do you tune it, or should i just block it and jet up. Thanks for any insight anyone has.
I’ll end up doing a specific video on secondary power valve tuning but what it really boils down to is the application and how it’s being used. I’ve generally removed them and gone to a bigger jet and smaller air bleed on a race carb.
@MuscleCarSolutions car is for street driving but not a daily fuel economy, not a massive concern. It's an original 4053 780 vac secondary, which i don't really want to modify, was thinking of getting rid of powervalve just to simplify tuning, then maybe put back and jet down once secondaries are operating correctly. Thanks for reply, look forward to videos.
Thanks for sharing the knowledge. My question cant be answered by anyone but the guy that installed a Holley Street Avenger 670 cfm on this 1983 GM 305 ci. That is, why is this 670 on this engine? I did not check the numbers on the heads, knowing that people like to install 350 heads on the 305, I should check that. That may answer that question. However, , specs. call for a 550 or 600 cfm on typical stock engines of the period. So, it idles great, it runs smooth through all driving ranges, but, it smells rich at idle. Primary jets are 65, power valve is 6.5. I intend to do the vacuum gauge trick you showedto determine engine to power valve requirements after I get the carb back together and installed. Mostly, my question is this, what is your take regarding the overall functionality of installing a 670 on a tired 305 ? The engine is installed in my 48 Plymouth, a back road cruiser car, all it needs is a 2 bbl. for that, but right now that option isnt available to me. What say you ?
A 500 would probably have been a better choice. The jets have nothing to do with fueling at idle. That’s what the mixture screws are for. Can you make that 670 better? Most likely. People generally don’t tune carbs. They just bolt them on and complain they aren’t perfect. 😆
I understand the PV number is when the PV starts to open, but I'm having a hard time understanding the spring rates since the spring collapses to keep the PV closed
First of all you explained it very well and understandable. I have a question though You said if you are getting a stumble after selecting a power valve some may increase accelerator pump swifter or speed and this will only mask the problem My question is then when is it appropriate to change accelerator pump speed and or squirter? Thanks
It’s a great question. We’re going to be doing quite a few tuning videos this summer with a 4150 series carburetor and that point for sure will be part of it.
I size my PV based on cruising vacuum and how much the vacuum drops as I accelerate. Example, if I have 12" cruising and it drop to 8" on accel, then I'll chose a 8.5. Never base PV size on idle, its not used there since the PV channels feed from the main well to the boosters.
It’s not a bad strategy for a street cruiser, but remember the PV is a transition circuit. That transition occurs off idle. That’s why the idle vacuum is generally the benchmark for setting the initial size.
First time rebuilding my Quick Fuel carb. I noticed on the Holly web sight that there are three brands of power valves, Demon, Holly, and Quick Fuel. Are these universal..? Can a Demon power valve be used in a Quick Fuel carburetor..? I'm obviously a novice at this...
Would the power valve have any effect off-idle? My 351 with 600 vac sec has on off idle stumble that I had attributed to the accelerator pump. By the way, it's worse when col, better when warm, so it's a lean mixture problem.
@@MuscleCarSolutions Idle in gear when warm (auto) is about 700rpm. I'm unsure how much advance I have in it, it's quite a lot as it's obvious when cranking, there is no detonation though even with lower octane fuel. I have no idea what PV Is in now. Not had the car long just starting to go through it
I have an '86 Honda Prelude in the UK and it shows symptoms that point to a malfunctioning PV based on what you are explaining. I know someone else who has the same symptoms on their Honda. Engine runs well from cold but then once heated up runs rough and revs drop down suddenly. I am thinking PV may be stuck?
Could be. Those cars are a little more difficult to diagnose. If it’s throwing a code you can sometimes scan it and it might tell you if it’s a rich condition. Or a quick swipe of the tail pipe will tell you if it’s sooty black it’s a rich condition. Pull a couple spark plugs also. Can at least give you an indication of what’s going on. I’m not familiar with that engine or fuel delivery system but if it’s still carbureted it will have an enrichment system like a power valve.
Many thanks for replying. The car is too old to throw codes up but all of the symtoms suggest it is the PValve. In the Honda manual (they had them then!), it shows how to test if there is a vacuum so i can get a cheap tester on Amazon or if i can locat the PV, as its not clear where exactly it is, I could swap from another Prelude that works. It starts well and is smooth as silk but once it warms up it drops revs, stalls and can backfire....
I remember a long time ago I was helping I think lol , a fellow with his bracket car . A 67 camaro . 427. Power glide ect .. it had think a 1050 holly . I fellow that had a record holding hemi car was parked beside us ...he asked what plugs . And then said install autolite . I pulled the carb carried it to the holly tech booth . The tech had power valves . Every one was a 2.5 . The tech installed the power valve , set the float levels , new gaskets ect. What a difference these things did . I never forgot..
I have a 351 Cleveland with 224 232 @ 50 cam 108 LSA with Holley 750 VS. When accelerating from cruise I note Vacuum goes from 17-10 Hg but not much lower. Afr goes from 13 to 17 and starts pinging. It currently has 6.5 power valve which I figure is useless. I think I need to go to a 10.5 power valve to get any enrichment. Does that sound right?
@rogerveal1336 correct, If going from a steady cruise to a slight Excell and vacum is only dropping to 10hg. Your not seeing any enrichment from your 6.5hg power valve. Iv also struggled to tune this window of power. Basically all happening on the primary side. My afr will be great at 45. Go to Excell still on primary only and my afr will jump up. Im Going to be playing with my pv a little myself.
I have bought a 750 Slayer for my 454 and it ran great but only 7 lbs of oil pressure, a little long in the tooth. I had the engine completely rebuilt and now it's a 461, it had no problems at all on the dyno and even tried an 850 CFM race carburetor and only picked up a few horsepower and torque. Put the engine in the car and I can't figure out what is going on? It will melt the tires! But I can't figure the stumble out for a life of me?
I think I understood if my car makes five pounds of vacuum which I got a pretty radical cam that would mean a 2.5 power valve but your suggestion for me to go to a 3.5 just trying to get clarification
If you run a 750 dbl pumper with mechanical secondaries do you run the same jet size in both meetering blocks? And should you have a power valve in both blocks?
i just testdrove a 68 chevy c20 with 4.56 rear gear ratio 4 SPD Manual. it idled in neutral fine and ran good at speed, although not very fast, it started screaming the engine to get to 60 mph. BUT maneuvering around corners and slowspeed driving WAS TERRIBLE. is that a malfunctioning accel pump or power valve or just a qwirk of 4.56 rearend? i couldnt buy if for this reason alone. and 2 nearby salvage yards have nothing for C10 rear axles to swap.
So I have a big overlap cam, 107 LSA. At idle, in drive I have about 4-5hg. At cruise it’s at 12(30mph, 14(40mph) 15.5(50MPH). I’ve tried a 6.5, 4.5, 3.5PV. The only issue I really see, is if I’m driving at 40-60 mph and hit the gas pretty good, it seems to break up, then goes. Could that be the PV? I know, I need an afr gauge. At the track, at wot it runs pretty much fine. It’s a 750 Proform race carb. I think 74 primaries, 80 secondaries( I think). Any input? TIA
I am happy to see that i am not the only one with a vacuum behavior exactly what you described. i always get confused when i hear "...you will have high vacuum at idle and the vacuum drops with raising (engine) speed" with my setup it is the exactly opposite. the same way you described. I dont know either what this means for this topic for choosing the right power valve. my impression is, my setup feels happier with higher PV-numbers like 8.5 compared lower like 4.5.
My sbc has the same problem! 5" of vacuum at idle without any vacuum leaks. Baffling! 110 LSA. Runs great just not much vacuum at idle? I'm not sure why? Any advice is appreciated.
@@Driven_Dragon not sure. but i suppose starting from a certain level of overlap, you just have to live with it. Maybe considering a little advancing of cam timing could gain some improvements. but i would expect too much of a change in idle-vacuum.
hi Ideally power valve engage at just above cruise ie vacuum reading at 45-50-55 mph . Then set the PV mixture thru the PVR power valve restrictor [PV screw in jet ] . Around 13 to 1 AFR The accelerator pump should be changed for stumble prior to that vacuum reading . Primary main jets RPM range 30---50mph set for around 14 --15 to 1 Afr readings at light throttle . Power valves are NOT unique to Holley
I worked for ford in the 70's ..we changed these things a LOT ... I am long retired from that ... I was wondering what the new ethanol fuel does to those power valves ??
Ethanol isn’t friendly to anything it comes in contact with. They have changed the materials to be a little more resistant to it, but it’s just a matter of time before the water and garbage that’s carried by it has some negative effect. Nature of the poor choice in fuel additive.
@@MuscleCarSolutions I was out of it when ethanol can in the picture ...worked around boats then and saw a lot of people having problems ...the 70's was the beginning of emission ...real emission controls ...the motors really suffered from it ...poor/bad idle and NO power ...
My car is exactly the same vacuum levels. I bought a 10.5 because I figured that is about where I would need extra gas when accelerating. The dividing by 2 thing is bad advice according to many. And I think they are right because they say a high number PV will make it run rich at idle. I have air fuel gauge and it doesn’t happen.
@@markmixon1121 yes right, some say that. but the PV-rating doesnt effect idle at all. As far as i know, the PV just enriches the primary circuit to the boosters but doesent effect the transition/idle-circuit. but i can be wrong.
I use to hear about something being off in the engine... The result was a backfire thru the Carb. When this happened it was said that the Power Valve can be blown due to this..... Any truth to that? Good Vid by the way.... I was thinking while watching, how hard it use to be to get this info..... Pre computer days. :)
Yes. Sometime in the 90s (I’d have to search to find when exactly) Holley started installing a check valve in the baseplate to fix the blown power valves on an engine backfire. So while it still does occur, it’s pretty rare these days. No doubt the internet has been a big positive on sharing information easier. With that though also comes the ease of sharing not so accurate info. 😆
That’s a topic we might cover in the future because few folks know how to read plugs to determine fueling issues. Maybe sometime this year when I get to some tuning videos.
Well, long duration cams weren’t designed to sit around and idle! Plug it and put more jet in and suffer with it. Or get a carburetor that allows you to add/remove fuel through the idle/intermediate and wot circuits.
I understand exactly what you are putting down. Was hoping youd have told me something i hadn't seen or heard of. Speaking of more adjustability, what are your thoughts on quick fuel carbs, ive been thinking of straying from my old reliable holleys and giving one a shot due to the ease of changing air bleeds compared to a traditional 4150dp
@jackball-lv5gt unfortunately Holley owns quick fuel now, so take that for what it’s worth. The new Edelbrock VRS is a FOUR circuit carb. Ridiculously inexpensive for all the adjustability you get from it, plus the auxiliary air bleeds. I did a full video on that carb if you’re interested in learning more.
Yeah, but you can tune it take to get to 4150 into it down to 500 if you use the right car valve in the right jet size and spring size and metering rod
I’m not understanding much of what you’re trying to say, but if I do understand what you’re saying, no. You can’t change the CFM of a carburetor. It’s fixed.
In all honesty the only thing I know about a power valve, or rather what I hear, is that a backfire through the intake will kill them. On a side not is it possible to tune a Holley to compare to a Q-Jet in terms of fuel economy?
Mid 90s(?) Holley put a check ball in the base plate to prevent a backfire destroying the PV. Unless it’s a really old carb, it’s likely fine. You’ll know pretty quickly if it isn’t! Short answer on fuel economy compared to a Qjet is no. There are way more design features on the Qjet to have better economy characteristics. That being said, if economy is really your goal, look to the transmission. You’ll find your biggest gains there. Especially if you’re currently running a 1:1 final drive transmission.
I put 780 meatering plates on my 650 carb with a 5 power valve with jets for a 850 carb and I got about 21 miles per gallon of gas as long as I didn't open the 4 bearel but when I stopped the gas pedal it would rip the rear wheels was wicked I still have the car the same engine and the same carb runs awasom
For all of the young people watching this, try to imagine growing up in the 70's and 80's, being 15 or 16 years old and trying to figure out this stuff before the internet and smart phones. My current carb (Since 2006) is a 1095CFM Demon. My cousin, (A younger, LS guy) refers to it as "A semi controlled fuel leak". Fuel injection is awesome, carbs are old school, I enjoy them both.
it was hard at the time to learn how to work on carburetors...
now imagine a young guy choosing carburetor over efi and making more power! that's me.
one of my close friends, a remaper, believed that carbs are worthless and not reliable to tune up to make power until he bought a peugeot 205 tu3 with weber carb on it, as he tested the car to see AFR with wideband sensor he have seen the most stable AFR ever on the whole rpm range of the engine, excat 13.5 to 1! he has quit making jokes out of my car since then.
i drive a peugeot 405, hand made engine (xu7 internal - xu5 cylinder head - xu9 camshaft - lightweigh flywheel and pulleys), 10:1 CR, 1800cc, aisan 2f carb, fantex delco and coil, magneti marelli ignition module.
my next project is to remove camshaft mechanical fuel pump and add high pressure/flow hearting pump.
Carbs may be old school but Id take them over efi any day on an older vehicle.....
I wish I did I tell people weekly I was born in the wrong era
Efi makes more power lower rpm, but the carburetor makes more in the higher rpms. Naturally aspirated, of course. There's many dyno videos that prove it. Younger tuners seem to hate it but numbers are numbers
Think about what it was like before you could buy off the shelf camshafts? My Dad used to grind his own back in the day (early 1960's) because there was no "performance store" available, you were it! there was know "knowledge base" to reference on profiles, ramp up, durations, degrees. You started with a piece of 2.5 bar stock!
At 65 I regret not seeing this invaluable information using the guessing game is not really fun. When I had it close, things would make me change my guesses, and then lose track of where I had just left off. Thanks for the encouragement!
I bought a new 600 cfm Holley from a guy that said he couldnt get it to run correct. I put it my vehicle and it did run rough. So i investigated and found out that the accelerator linkage cam was set incorrectly. Reset it and it preformed great.
@@rogerbeck3560 good deal. Now tune it and really make the engine and your driving experience better! 👍
I have a feeling that a carb tuned by you would be just as good as a Holley sniper unit without worrying about electronics leaving you on the side of the road, keep the videos coming
Lots of time and years making a bunch of mistakes! But I do enjoy the process and the outcome. Good times!
But a sniper will adjust your air fuel ratio while you’d have to get out and change jets pretty regularly to keep up…
@@patrickharper9297 good point for sure
@@patrickharper9297 why would you change Jets regularly? Unless you modify the car once you get it jetted right its done. The worst I've ever had to do is just adjust the mixture screws at idle when the weather changes or I do a tune up.
@@patrickharper9297 maybe if going to higher altitude or cold or hot weather, but that’s about it
love the break down on power valves , a lot harder to change when you have multiple carbs like a six pack.
or Webers!
I remember the days long before AFR gauge availability... the way to tune any carburetor was to read the spark plugs, the use of a vacuum guage, seat of the pants feel(butt dyno) and to get a better handle on tuning for max power, was to take your car to the 1/4 mile track and adjust accordingly.
Now you plug your laptop in and push a couple of buttons. People now a days don't know how to "really" tune car
@@rickkutyla251 sure but they are tuned better.
Good times!
Most people problem was their ears & butt dyno got very comfused once the time clocks popped up! They always thought the bigger the cam sounded the faster it was! And it would be ok as long as it was blowing the tires off!
I love your Carburetor tech videos. When I get stuck or question something I search them
Appreciate that! Hope they’re helping!
Ford carbs used the same valves on 2 barrel and 4 barrel flat top carbs in the 60s and 70s. Worked on a lot of them. Ford called it an economists valve. Found below the float bowl. Turn the carb over and under a cover held on with 4 screws holding the cover.
Inspection plugs in the exhaust... and chaining the front down and putting it in gear accelerating in a pull to set the timing.... Crazy as you may,,, it works.😜 I always loved a Quadrajet ....but it's what I knew but once I started messing Holley I was impressed....Fuel injection is much more Simple.... once you learn... After all my rambling..... Very informative Video content... thanks
fuel inj. wayayy easier...got over 300hp on the dyno with all stock internal original oem parts on my 2.0 4g63
This is the best explanation of how to tune a carbonator I have ever seen. Great job
Glad you enjoyed it!
I remember the 67 Chevy Caprice with the Big block 427 had a factory vacuum gauge and there was others in a long them year's also had factory vacuum gauges....A crucial measurement.. I also installed inserts in the manifold and or Header's back in the day to read the color of the exhaust Flame..... other little tricks putting the car under load while setting timing and there are many other recurve Kit's and on and on..... Very good content here😎
Holley used to recommend a different process for PV.
**Automatic timing & idle set, engine operating temp, “In Gear”:
Vacuum hg minus 2hg= base PV.
**Manual transmission timing & idle set, operating temperature: Vacuum hg divided by 2= PV.
Exactly
Holley recommends half idle vacuum as a starting point, and sometimes adding 2" to that number
I'll just correct one thing you said at around 5.30 ...you mentioned the vacuum hits the diaphragm which overcomes the spring letting fuel to pass...actually the other way around...vacuum holds the valve closed then when vacuum drops under load the spring opens the valve allowing fuel to flow...when vacuum recovers it overcomes the spring and closes the valve again. I'm guessing that was what you might have meant?
One needs to realize that the idle mixture (AFR) will be unaffected by whether the PV is open or closed. This is because the fuel admitted from the PV feeds into the PVCRs at bottom of the main fuel wells; at idle, the main circuit has not started as evidenced by the fact that there should be no fuel flowing from the boosters. When the PV should open is when the engine load increases decreasing the engine vacuum such as going up an ever-increasingly steep hill or opening the throttle under load. In other words, the PV should open when the mixture starts to become lean (or 2" Hg vacuum prior to this point) under load to enrichen the mixture. Although the guidance of "idle vacuum divided by 2" may work in many cases, it is better to establish when the mixture starts to go lean and then add 2" to this point to select which PV to use.
I like your info. Makes sense to me. But when do you know when you’re 2” hg before lean condition? The air fuel ratio and vacuum reading will change rapidly at say, a launch at a drag strip. How do you determine the point to choose the valve?
Ohhhhh, yes! Thank you for another great and informative vid. It seems like the power valve is often overlooked. Great tips, especially with the right size carb. Be it car, truck or motorcycle, you're right, it's often a setup with a carb that is too big. Thanks!
Indeed! It doesn’t get enough credit for how it helps the carburetor to operate for the intended use. No doubt on too big being too common! Thank bud!
I was surprised you didnt go over how the early holleys didnt have power valve savers and when the engine backfired it would blow the power valve diaphragm out and it would just mess up everything. I used to drill out the power valve channel and install check valves but holley does that now..!! Lots of good info ...!!
Time. Time dictates everything. If I include too much information, folks seem to get spicy about it. So I try to compact it all in and not go down every possible rabbit hole on a topic. That’s difficult to do sometimes! Thankfully Holley fixed that issue in the 90s cuz back in the day… we changed a LOT of blown power valves. 😂
@@MuscleCarSolutions 🤣🤣🤣 You got that right.
This is good general information it would be good to pinpoint some common scenarios on Holley carburetors. The problem I found with most Holly's is cruising down the road they are usually too rich like 11 to 1 but under wide open throttle they are very close 12.8 to maybe 1 3. To get that cruising air fuel ratio 14 to 1 and then have a good tip in plus wide open and then idling is very difficult to achieve
Would love to include everything in one video but 20-25 minutes seems to be the tipping point. Any longer than that and people just don’t watch. Or they complain nonstop that the video was too long. 😆 I have more planned. We’ll eventually cover everything.
I have found most guys put larger front jets in to get rid of the lean stumble that occurs while cruising and trying to gain a few mph. They should’ve corrected the stumble with a power valve as described in this video.
The issue is with the words Holley uses when you’re using their Hot Line because they say the Power Valve is a power adder. This wording plays with your head because, okay yeah it adds extra fuel just before the lean stumble occurs adding power to gain or maintain the speed you’re cruising at.
So the guys only want it to quit stumbling when they’re out cruising and already have the great track times, so now they jet up the front jets like Holley tells them making the cruise mixture rich and then when you go WOT everything is great.
If you adjust the cruise mixture using an O2 sensor you end up putting the original jets back in and sometimes one size larger (due to the ethanol added in the fuel) and then make the driveability correction with a power valve that opens just before the lean stumble occurs. You want the power valve to open at least one inch of vacuum higher than the stumble occurs.Have someone watch the vacuum gauge and when the needle suddenly drops to 0” say at 7.5”. Install a 85 Power Valve.
Thanks explained well without talking down to me
Hi! I am a new subscriber. I am very new to this and found out I know nothing! Lol! I am going to lean as much as I can. Thank you for sharing the knowledge
They were known as economy valves many years ago. Two stage power valves were great. The problem is that most people did know anything about power valves to begin with. This valve was for those who understood on how to use them.
Biggest problem with holly carbs is people tune them completely wrong. They have a reputation for being thirsty and not good for the street. The main jets control the cruise mixture, and the PVRCs control the WOT mixture. Sure in a race application go ahead and block the power valves off and set the WOT mixture with the main jets. As for a street application no matter if it’s a 200 HP bone stock 6 cylinder or a 1000 hp monster you NEED metering blocks with replaceable PVCRs, air bleeds, idle jets, and emulation tube jets. A 4150 or 4500 holly can be tuned to give great results throughout the RPM range and at different throttle openings. Jet the carb for the leanest possible cruise mixture that allows smooth engine operation with the main jets. Then jet it for max power with the PVCR jets. Granted tuning a holly style carb is a bigger pain in the ass then a Weber or Carter style carb because you have to pull the bowls, metering blocks and power valves to make adjustments, however they can be tuned to deliver the same air fuel ratios under the same conditions. Your best bet is to try and find a set of those wonderful metering blocks for the 4150 that take Weber calibration parts! Those blocks were wonderful because you could tune the carbs as easily as a downdraft Weber including changing jets without even shutting down the engine! No idea why they stopped making them but If you can find a set grab them!
Great video best one out there easy enough to try two different ones if you don't have AF readings then you find what it likes depend on camshaft overlap selection bottom line more cam less vacuum
All good information.... of course we have more questions. With a Manual transmission, the vacuum varies. Add in a draw through turbo setup, and im scratching my head as usual. I see a rich condition under load for sure...and sometimes a lean condition depending on gear im in at the time. and cant seem to jet it down (or up) far enough to fix this. The power valve is my next direction. I assume you will see the power valve open on your AFR gauge. I need to pay more attention to this. Thanks for the tips
A video on tuning the 4150 for two step launches, would be a great topic.
Not sure we’ll get there anytime soon. Though I am itching to get back into another drag car. With the drag and drive events so popular now, that might be on the list to build some day soon.
Or the difference on tuning a carburetor on boost and nitrous applications
I use a air fuel meter and vacuum gage to tune mine. Main jets for air fuel ratio of 14-1 at 2500 driving down the road and the power valve vacuum setting for when it leans out. Right now running 69 jets and 2 inch power valve on a 500 cfm 2 barrel .
From my understanding and studies, the purpose of the power valve is that it allows you to cruise (pretty much at any speed) and you want it to remain closed. You only want to open the flow and enrich when under larger power demands like spirited acceleration and/or WOT. PV's allow the carb to downsize the main jet about 7 numbers vs no power valve so that you can cruise and sip fuel. So where I get a little lost in this video is the various cruise tests. I would be reading those vacuum readings and making sure I chose a PV which is closed under all of those cruise conditions. I am learning all I can and working hard trying to tune multiple holleys to get one working well on my hot 327SBC, but I can't say I'm doing so well yet. Using vacuum, wideband, tach, and video recording gauges and trying..... Have a horrible lean condition on throttle tip in.
Speed is the easiest way to help understand opening events and driving data. It’s easy because we can work with something everyone can measure like MPH. Load, no so much. Looking at this I could have done a better job of explaining the why. If I could, I’d just have everyone run a data logger and we can see the full run and when those lean/rich condition occur. For sure when we start doing tuning videos on both my truck and Chevelle, we’ll walk through the process with more clarity. Thanks for the note. Very helpful.
One of the things that make a huge difference is in gearing. My car no overdrive with 3.25 gears high stall you cant lug it. Hard to get vacuum to drop much during normal driving. Now put an overdrive it, a heavy car with a lockup torque convertor and every hill you go up vacuum will drop a lot. I try to size the vacuum opening for normal driving so it stays closed. But I'm trying to run around 14-15 fuel ratio. If it pings due to lean or advance timing you could cover it by opening the power valve just before the ping. Great video. I do have a data logger.
I would go with annular boosters instead of straight or dog leg boosters. The lean tip in at cruise speed is either the transition circuit going lean before booster take over or insensitive boosters not activating soon enough. Carb size problems are really just booster and emulsion problems.
Looking forward to your reports about tuning the edelbrock 4150. I will tune right along with you since I have my own edelbrock 4150 that I will try out on my current engine build. And I have a lot to learn.
Very cool! Thank you. For sure we’ll be tuning the 650 on my GMC and later on when the big block is done on the Chevelle we’ll be tuning an 850 on it. Lots to cover between now and then! I’ll be doing more content on the 4150 series carbs very soon.
Awesome video man thanks for the tips. I love the buy a little 2 1/2 inch vacuum gauge for my car.
Great breakdown on power valves, and dialing them in! I subbed!
There is no such thing as a carburetor that is too large.
The emulsion well is the least understood area of ALL carbs, not just holley's.
You described power valve operation precisely backwards. Engine vacuum keeps the valve CLOSED, not open. The power valve channel restrictor under the valve should be used to tune WOT operation and the main jets used to tune cruising A/F ratio.
I disagree, if the carb is capable of more air than the engine will ever need or use then its too big. You can argue that a 4 cyl can run with a 1000 cfm carb which is true but nobody sane thinks it would run well.
@@cuzz63 it's easy to take anything to absurd extremes to prove a point. Even if it's a spurious or specious point.
@@psychoholicslag4801 So then why the comment? We all know that at a certain point a carb can be too big.
@@cuzz63 not within the context of the video. Just putting a high capacity carb on a tiny engine was not the discussion. Design of the carb circiuts was and a carb of the correct design would work well. However using just any carb would not work well. Most carbs are chosen using the wrong criteria as in it's rated flow rate instead of the booster design and fuel curve needed. Most dyno tests for carbs are really booster tests. For example, an I R type system with 300 CFM per carb will make more low speed torque than a small 4 barrel on a 302 cu inch v8. Why? Because the flow rate isn't the issue, the atomization of the fuel due to internal design is.
This is an interesting discussion. I've done my share of Holley carb tuning rebuilding over the years. 100's of them.
If I take a Holley plug the power valve, a part is specifically made for this, I will get better gas mileage. I see no noticeable difference in performance.
But then, I'm not massing the throttle to the floor but driving normal.
So the only thing I infer is the power valve still dumps fuel even under no load.
Excellent Video ! Simple to understand ..
I’ve always gone 2 sizes below manifold vacuum in drive. It gives instant response and no stumble.
That’s one way to do it, but any method is only a starting point. Not a single adjustment.
Im confused on your manifold vacuum theory. To my understanding manifold vacuum decreases the more open the throttle is. That would make the valve function the opposite way that you explained it.
Hello, good video, very good explanation, you touched on a topic where you mention a carburetor with very high cfm for a very small engine. I will be waiting when you explain the physical difference from an 850 cfm to 650 cfm for the street and how to try to correct it. Thank you.
This video got my sub 👍 Look forward to checking more once I get running and gleaning all I can, thank you for them !
Will be doing quite a few more 4150 carburetor content this year. Hopefully you’ll find them useful too!
I fought the concept of fuel injection about as hard as I fought the concept of buying CD's instead of vinyl records, but with fuel injection, I didn't have all the trial and error, test runs, driving conditions, and removing the float bowl assembly to get to the metering block and jets every time it needed adjustment. You just plug in the laptop and tell it where to add/remove fuel at a given load or RPM. I love the simplicity of carburetors, but the tuning takes skill and patience that most old school rodders don't bother with, and just settle for a close, off the shelf carb.
@@stephencarr7173 that’s very true. The trouble with carburetors is people get used to how bad it runs because it may start fine and maybe operate ok at WOT so they assume it’s good. They learn to put up with rich conditions, fouled plugs, contaminated oil, the garage stinking of fuel, burning your eyes out standing behind it at idle…every bad operation they just accept. It’s a carburetor, that’s the way they work. NO! It’s one of the reason why I started this channel. For gods sake tune that thing and realize it’s full potential! EFI is a whole other ballgame. Wait till I start doing more tuning videos on those. 😉
Too bad about the two stage power valve. I tuned my 650 DP using one. It allows a leaner cruise mixture for economy and the first stage takes the flat spot out when pulling hills and keeps the full metering block restrictions from opening. Better drivability, better control of the mixture. Std equip on an 85 GT 5.0L mustang. Not looking forward to the day it fails.
Great presentation and info feller
So help needed. I have a ATM Innovations XRSB-750. I'm running really rich 11.2 at idle and 14.0 at cruising speed. The fuel is pushing out of the exhaust at Idle and wanting to die upon any acceleration. For context I have pump nozzle of 31 primary and secondary 35 high speed bleeds 70 idle air bleeds .78 primary main jet and .93 secondary, 33 idle feed restriction, 2.5 power valve and 110v needle and seat. Timing locked out at 38 with 7.5 psi of fuel pressure that can be regulated down if needed. My question is what changes do i need to make to fix the off idle stumble/car completely dyeing or choaking out and the extremely rich low end. Thanks in Advance
This is very good. if you have a "fully" adjustable carb as the new Edelbrock 4150 or one like it and you have an dual ARF gauges (v8, 1 for left and 1 for right & dual plane manifold), vacuum gauge and a human data logger. How do you know what to change? power valve, PV restricter, high speed, low speed air bleeds, air bleed restrictor, etc. I get if AFR reads lean at X RPM I need to add fuel to a circuit that affect that RPM. I've read the Holley red book on 4150/4160 and David Vizard's Super Tune and Modify Holley Carbs book. I'm having trouble turning words and pictures into practice. I've probably read what I need to know and didn't realize it, so maybe hearing it another way would turn the light bulb on.
I’m going to do quite a few videos in this once the big block for the Chevelle is done. It’s an extremely long process and very very technical. But you’re spot on that a dual wideband O2 will be extremely helpful. Absorbing good tuning information online for sure will help. The good things is as long as you don’t go too lean, it’s something you can tweak on your own and learn as you go. Just take really good notes along the way. What your AFR readings were at the rpm you’re monitoring and what your changes were. That way you can always go back if you get too deep into the weeds.
If your engine is cammed up, don’t be surprised if you have to use a 105 Power Valve and install one size larger front jets than what came in the carburetor stock when using Premium gasoline that has the 15% ethanol.
Hey you put out some very informative videos. Just a question or two if you don't mind. What would the 30, 40, 50 and 60 MPH show me on my vacuum gauge and my wideband? I understand the vacuum will drop but at what steady speed should the PV kick in? Or am I misunderstood something? Maybe you could do a video (I'm sure it would help a lot of us) on exactly how and when the jets work, how and when the squirters kick in and for about how long. How and when the PV kicks in and when should the secondaries kick in on the jets and/or the PV. Or do the jets along with the PV on the secondary side kick in exactly at the same time? Sorry if I'm going overboard but that would explain a lot, especially to me.
the PV shouldn't kick in at any steady speed. it should kick in when you leave cruise mode and move to acceleration situation.
i guess, what it was tried to explain, that if you monitor your engine in different steady speeds, then watch to which rating the vaccuum drops when you then want to accelerate and choose your PV near that point
Question? Am I correct is saying that if the rating of the Power Valve is lets say a 6.5 and that's higher than the idle vacuum at 5 inches of vacuum at 900rpm the engine will run too rich because the Power Valve is Open, and if the Power Valve is a 2.5 the engine could run lean until the engine vacuum is below 2.5 inches of vacuum? On this new build I have a new AED 750dp on a Chevy 302ci with 10.5 compression, Comp Cams custom grind solid flat tappet with .516 intake and .537 exh lift with 242 intake and 250 duration @ .050 and with a 110 lobe separation, valves set to .012 cold, new MSD ignition and pro-billet distributer, Victor Jr intake, AFR 180 Street Heads bolted to 1-5/8" headers to 3" flowmasters. It mated to a M21 trans and 3.90 gears on a 28" tall tire. I had the timing at 19* initial and 36* with the same problem but my Brother told me it was too much for 91 pump gas so I lowered it to 13* btdc initial at idle and 32* total. Plugs are all consistant light tan color as well.
The problem I'm having is an intermittent lean pop and low power through the carburetor when under load accelerating in 1st gear under 3k rpm and inconsistent idle rpm when warm to operating temperature. I'm at 1-1/2 turns out on the Air/Fuel screws, accelerator pumps adjusted properly with cams in the #2 position. I just opened the secondary butterflies because too much of the idle slot was showing from the underside of the primary butterflies (this did help the idle but is lower idle at operating temperature than when warm). The standard squirters are 31's as well. The vacuum at 900 rpm is at 5 inches so I put a 2.5 power valve in it and didn't think about it much until I watched your videos on this subject. I'm thinking I should have a 4.5 power valve. Am I on to something here or what else can I check or adjust? BTW, above 4k rpm it's an ANIMAL for a 302! Thoughts?
Does any of the vacuum gauge tuning advice change for an airboat application since it is always in gear and under load due to the prop spinning at idle?
Having EGT's will also help you tune your carburetor when it comes to putting in the right jet sizes
It’s not a preferred tool, but it can be beneficial if you’re tuning for economy. I’d rather have the rifle shot accuracy of an AFR.
6.5 Holly genuine power valve allways seemed to be the best all-around
@@v1-vr-rotatev2-vy_vx31 no such thing when tuning. If that were the case, there would only be one size!
How do you adjust with 2 power valves? Do you run a smaller one on the primary and a bigger one on the secondary if its vacuum secondary or run them the same size?
Good explanation
Would like tuning tips on a edelbrock 2.o street tunnel ram with two holly 600 cfms vacuum secondary, 454 bb chev , 400 turbo , 3.50 gear set
I have a old 600cfm 4160 on a ford 289 and at half to full throttle it’s way rich idle is good but regardless of how much tuning I do I can’t get it to lean out at part and full throttle. It has a 6.5 power valve that came with the kit.
Tried a smaller valve?
@@MuscleCarSolutions well I’ve been thinking about it. Warmed up it reads about 15 inches of mercury. It has a small cam in it. So I’ve been trying to figure out what size power valve I should get. And at those throttle positions, the AFR‘s bounce between 12 and 10.
Well at half throttle the PV should be open. So try a smaller PV and see if it leans that condition out. Try a 5.5 next and see how it does. If it gets better but not perfect, try a 4.5. Start with the 5.5 though. Make small steps. If that helps, then you’re on your way and retune. The 600 is probably too much carb, especially if that’s a mostly stock 289, so you’ll not get it perfect but you can make it better.
@@MuscleCarSolutions ok thank you
I run a vac gauge inside my cowl. I got 15 inches at idle had to go with a 9.5 pv to get right afr at like 1/3rd throttle
Excellent!
What is your opinion on a PV choice when the cam has a lot of overlap down low with low vacuum? Cruising speed has good vacuum tho. I get 8 to 9 inches of vac when in park and drops to 6 when in drive. I'll get over 12 at cruise.
@@FrankenVega always a bit of a moving target. AFR makes it easier but in absence of that, I’ll generally start with a numerically lower size and adjust up. Won’t take long to figure out when it’s supposed to hit and when it’s awful. I’d start with a 4.5 and move up from there.
throttle position and inches of vacuum [load ] tell u when the mixture occurs . An Air/fuel gauge tells u how much [quanity] fuel.
Advanced tuning methods a vacuum gauge can do both
What about dual carburetors for power valve ?
Tuning video for another day.
Great stuff
so when you are checking engine vacuum at 30, 40, 50 and 60 mph - do you take that number and use it for the power valve, or do you still divide it by 2? Thanks!
More so I know when it opens. With that info you can verify if you want it to open sooner or later.
Thank you, sir.
Ok. So. Suppose you have 9-10" of vacuum at idle and you go all the way up to a 8.5 power valve and you still have a tiny hesitation at around 9" are you supposed to go to a 10.5 p/v? Or play with cams and accelerator pump shots? At what point does that come into play?
If you're still responding to this video. It sounds like the higher the power valve number the sooner it opens?? Maybe it sounded like the lower the rpm the more vacuum so a higher rated power vacuum is needed. Something sounded backwards. I think where you said the engine will see 4.5 vac before it sees 3.5 is where I got confused.
Go and rewattch the video. 12:30 is what you are referring too.
When you go WOT the vacuum drops down. If you have 8 inches of vacuum at idle, you divide that # in half, which would be 4. So your choice is a 3.5 or a 4.5 power valve, they don't make a 4.0
A 4.5 pv will allow fuel earlier than a 3.5 pv as the vacuum drops. If the carb is on the rich side, then I'd try the 3.5 pv which would help lean it out in that scenario.
Good stuff thanks
Great vid as always, this may be a stupid question, but I've looked around a bit and haven't found a good answer. Power valve in secondaries, is there an advatage if so how do you tune it, or should i just block it and jet up. Thanks for any insight anyone has.
I’ll end up doing a specific video on secondary power valve tuning but what it really boils down to is the application and how it’s being used. I’ve generally removed them and gone to a bigger jet and smaller air bleed on a race carb.
@MuscleCarSolutions car is for street driving but not a daily fuel economy, not a massive concern. It's an original 4053 780 vac secondary, which i don't really want to modify, was thinking of getting rid of powervalve just to simplify tuning, then maybe put back and jet down once secondaries are operating correctly. Thanks for reply, look forward to videos.
Great video. New here, but I can see you really know and enjoy cars. Thank you
Thanks for sharing the knowledge. My question cant be answered by anyone but the guy that installed a Holley Street Avenger 670 cfm on this 1983 GM 305 ci. That is, why is this 670 on this engine? I did not check the numbers on the heads, knowing that people like to install 350 heads on the 305, I should check that. That may answer that question. However, , specs. call for a 550 or 600 cfm on typical stock engines of the period. So, it idles great, it runs smooth through all driving ranges, but, it smells rich at idle. Primary jets are 65, power valve is 6.5. I intend to do the vacuum gauge trick you showedto determine engine to power valve requirements after I get the carb back together and installed. Mostly, my question is this, what is your take regarding the overall functionality of installing a 670 on a tired 305 ? The engine is installed in my 48 Plymouth, a back road cruiser car, all it needs is a 2 bbl. for that, but right now that option isnt available to me. What say you ?
A 500 would probably have been a better choice. The jets have nothing to do with fueling at idle. That’s what the mixture screws are for. Can you make that 670 better? Most likely. People generally don’t tune carbs. They just bolt them on and complain they aren’t perfect. 😆
I understand the PV number is when the PV starts to open, but I'm having a hard time understanding the spring rates since the spring collapses to keep the PV closed
First of all you explained it very well and understandable. I have a question though
You said if you are getting a stumble after selecting a power valve some may increase accelerator pump swifter or speed and this will only mask the problem
My question is then when is it appropriate to change accelerator pump speed and or squirter? Thanks
It’s a great question. We’re going to be doing quite a few tuning videos this summer with a 4150 series carburetor and that point for sure will be part of it.
I size my PV based on cruising vacuum and how much the vacuum drops as I accelerate. Example, if I have 12" cruising and it drop to 8" on accel, then I'll chose a 8.5. Never base PV size on idle, its not used there since the PV channels feed from the main well to the boosters.
It’s not a bad strategy for a street cruiser, but remember the PV is a transition circuit. That transition occurs off idle. That’s why the idle vacuum is generally the benchmark for setting the initial size.
Great video 👍🇦🇺
Does power valves come as a adjustability options? Like a flat screw driver head on the power valves?
I am now thinking of a blow through carburetor.
There are boost referenced power valves for blower applications.
First time rebuilding my Quick Fuel carb. I noticed on the Holly web sight that there are three brands of power valves, Demon, Holly, and Quick Fuel. Are these universal..? Can a Demon power valve be used in a Quick Fuel carburetor..? I'm obviously a novice at this...
They are the same.
Would the power valve have any effect off-idle? My 351 with 600 vac sec has on off idle stumble that I had attributed to the accelerator pump. By the way, it's worse when col, better when warm, so it's a lean mixture problem.
It’s possible. What PV is in the carb now? But I’d start with some other things first. What’s your timing set at? What is your idle rpm set to?
@@MuscleCarSolutions Idle in gear when warm (auto) is about 700rpm. I'm unsure how much advance I have in it, it's quite a lot as it's obvious when cranking, there is no detonation though even with lower octane fuel. I have no idea what PV Is in now. Not had the car long just starting to go through it
Your input is good 2 hear good stuff.
Thank you sir. Hope the winter weather wasn’t in your area out there!
@@MuscleCarSolutions lot of rain no flooding, I can C snow on the mountains. 👍
@@VinoRatRodbuilds glad to hear it hasn’t affected you too bad!
I have an '86 Honda Prelude in the UK and it shows symptoms that point to a malfunctioning PV based on what you are explaining. I know someone else who has the same symptoms on their Honda. Engine runs well from cold but then once heated up runs rough and revs drop down suddenly. I am thinking PV may be stuck?
Could be. Those cars are a little more difficult to diagnose. If it’s throwing a code you can sometimes scan it and it might tell you if it’s a rich condition. Or a quick swipe of the tail pipe will tell you if it’s sooty black it’s a rich condition. Pull a couple spark plugs also. Can at least give you an indication of what’s going on. I’m not familiar with that engine or fuel delivery system but if it’s still carbureted it will have an enrichment system like a power valve.
Many thanks for replying. The car is too old to throw codes up but all of the symtoms suggest it is the PValve. In the Honda manual (they had them then!), it shows how to test if there is a vacuum so i can get a cheap tester on Amazon or if i can locat the PV, as its not clear where exactly it is, I could swap from another Prelude that works. It starts well and is smooth as silk but once it warms up it drops revs, stalls and can backfire....
I remember a long time ago I was helping I think lol , a fellow with his bracket car . A 67 camaro . 427. Power glide ect .. it had think a 1050 holly . I fellow that had a record holding hemi car was parked beside us ...he asked what plugs . And then said install autolite . I pulled the carb carried it to the holly tech booth . The tech had power valves . Every one was a 2.5 . The tech installed the power valve , set the float levels , new gaskets ect. What a difference these things did . I never forgot..
Interesting stuff.
I thought you were talking about 2 stroke power valves from the title. Lol😂
using the rpm might be easier , drive at 30 or 40mph on the right gear, check rpm, check vaccum at that rpm when stopped and get a reading
I have 6.5 pv and seems extremely rich a cruise 2000 rpm manifold vacuum is little low this gives me a place to look
AWESOME VID !!!! A++++
I have a 351 Cleveland with 224 232 @ 50 cam 108 LSA with Holley 750 VS. When accelerating from cruise I note Vacuum goes from 17-10 Hg but not much lower. Afr goes from 13 to 17 and starts pinging. It currently has 6.5 power valve which I figure is useless. I think I need to go to a 10.5 power valve to get any enrichment. Does that sound right?
@rogerveal1336 correct, If going from a steady cruise to a slight Excell and vacum is only dropping to 10hg. Your not seeing any enrichment from your 6.5hg power valve. Iv also struggled to tune this window of power. Basically all happening on the primary side. My afr will be great at 45. Go to Excell still on primary only and my afr will jump up. Im Going to be playing with my pv a little myself.
@@jacobsantilli7369 10.5 power valve fixed it.
I have bought a 750 Slayer for my 454 and it ran great but only 7 lbs of oil pressure, a little long in the tooth. I had the engine completely rebuilt and now it's a 461, it had no problems at all on the dyno and even tried an 850 CFM race carburetor and only picked up a few horsepower and torque. Put the engine in the car and I can't figure out what is going on? It will melt the tires! But I can't figure the stumble out for a life of me?
Where is it stumbling? Off idle? Mid range? What carb does it have on now? What’s your timing set at?
I think I understood if my car makes five pounds of vacuum which I got a pretty radical cam that would mean a 2.5 power valve but your suggestion for me to go to a 3.5 just trying to get clarification
It’s a starting point. Pick one and see how your drivability is. Adjust from there.
If you run a 750 dbl pumper with mechanical secondaries do you run the same jet size in both meetering blocks? And should you have a power valve in both blocks?
i just testdrove a 68 chevy c20 with 4.56 rear gear ratio 4 SPD Manual.
it idled in neutral fine and ran good at speed, although not very fast, it started screaming the engine to get to 60 mph.
BUT maneuvering around corners and slowspeed driving WAS TERRIBLE.
is that a malfunctioning accel pump or power valve or just a qwirk of 4.56 rearend?
i couldnt buy if for this reason alone.
and 2 nearby salvage yards have nothing for C10 rear axles to swap.
So I have a big overlap cam, 107 LSA. At idle, in drive I have about 4-5hg. At cruise it’s at 12(30mph, 14(40mph) 15.5(50MPH). I’ve tried a 6.5, 4.5, 3.5PV. The only issue I really see, is if I’m driving at 40-60 mph and hit the gas pretty good, it seems to break up, then goes. Could that be the PV? I know, I need an afr gauge. At the track, at wot it runs pretty much fine. It’s a 750 Proform race carb. I think 74 primaries, 80 secondaries( I think). Any input? TIA
I am happy to see that i am not the only one with a vacuum behavior exactly what you described. i always get confused when i hear "...you will have high vacuum at idle and the vacuum drops with raising (engine) speed" with my setup it is the exactly opposite. the same way you described.
I dont know either what this means for this topic for choosing the right power valve. my impression is, my setup feels happier with higher PV-numbers like 8.5 compared lower like 4.5.
My sbc has the same problem! 5" of vacuum at idle without any vacuum leaks. Baffling! 110 LSA. Runs great just not much vacuum at idle? I'm not sure why? Any advice is appreciated.
@@Driven_Dragon not sure. but i suppose starting from a certain level of overlap, you just have to live with it. Maybe considering a little advancing of cam timing could gain some improvements. but i would expect too much of a change in idle-vacuum.
hi
Ideally power valve engage at just above cruise ie vacuum reading at 45-50-55 mph . Then set the PV mixture thru the PVR power valve restrictor [PV screw in jet ] . Around 13 to 1 AFR
The accelerator pump should be changed for stumble prior to that vacuum reading .
Primary main jets RPM range 30---50mph set for around 14 --15 to 1 Afr readings at light throttle .
Power valves are NOT unique to Holley
Great video!!
Thanks bud. Hope you’ve been well.
@@MuscleCarSolutions Yes sir. Got a new toy for the channel. Coming soon.
@@hybridmusclegarage4590 can’t wait! Will keep an eye out for it! 👊
I worked for ford in the 70's ..we changed these things a LOT ... I am long retired from that ... I was wondering what the new ethanol fuel does to those power valves ??
Ethanol isn’t friendly to anything it comes in contact with. They have changed the materials to be a little more resistant to it, but it’s just a matter of time before the water and garbage that’s carried by it has some negative effect. Nature of the poor choice in fuel additive.
@@MuscleCarSolutions I was out of it when ethanol can in the picture ...worked around boats then and saw a lot of people having problems ...the 70's was the beginning of emission ...real emission controls ...the motors really suffered from it ...poor/bad idle and NO power ...
I just bought a mercury cougar with a turbo charged 302ci in it. It’s running very lean. I don’t know anything about it and I’m lost.
What about a bigger cammed car? I get about 7 at idle but when cruising it’s around 14. Am I setting the power valve half of 7 or half of 14?
My car is exactly the same vacuum levels. I bought a 10.5 because I figured that is about where I would need extra gas when accelerating. The dividing by 2 thing is bad advice according to many. And I think they are right because they say a high number PV will make it run rich at idle. I have air fuel gauge and it doesn’t happen.
@@markmixon1121 yes right, some say that. but the PV-rating doesnt effect idle at all. As far as i know, the PV just enriches the primary circuit to the boosters but doesent effect the transition/idle-circuit.
but i can be wrong.
@@rustonwheels3064 we on the same page.
Thank you. Clears up a lot.
I use to hear about something being off in the engine... The result was a backfire thru the Carb. When this happened it was said that the Power Valve can be blown due to this..... Any truth to that? Good Vid by the way.... I was thinking while watching, how hard it use to be to get this info..... Pre computer days. :)
Yes. Sometime in the 90s (I’d have to search to find when exactly) Holley started installing a check valve in the baseplate to fix the blown power valves on an engine backfire. So while it still does occur, it’s pretty rare these days.
No doubt the internet has been a big positive on sharing information easier. With that though also comes the ease of sharing not so accurate info. 😆
What about reading spark plugs?
That’s a topic we might cover in the future because few folks know how to read plugs to determine fueling issues. Maybe sometime this year when I get to some tuning videos.
What if your fighting the Power valve opening at idel due to long duration camshaft, persay 5" at idle
Well, long duration cams weren’t designed to sit around and idle! Plug it and put more jet in and suffer with it. Or get a carburetor that allows you to add/remove fuel through the idle/intermediate and wot circuits.
I understand exactly what you are putting down. Was hoping youd have told me something i hadn't seen or heard of. Speaking of more adjustability, what are your thoughts on quick fuel carbs, ive been thinking of straying from my old reliable holleys and giving one a shot due to the ease of changing air bleeds compared to a traditional 4150dp
@jackball-lv5gt unfortunately Holley owns quick fuel now, so take that for what it’s worth. The new Edelbrock VRS is a FOUR circuit carb. Ridiculously inexpensive for all the adjustability you get from it, plus the auxiliary air bleeds. I did a full video on that carb if you’re interested in learning more.
Many people think engines bog because they have too much fuel. Such is rarely the case. A little rich rarely causes bog/hesitation.
I used to get 21mpg in a 77 Pontiac g/p with a 280 duration cam in a 400. Go holley.
😂😂😂😂😂
Yeah, but you can tune it take to get to 4150 into it down to 500 if you use the right car valve in the right jet size and spring size and metering rod
I’m not understanding much of what you’re trying to say, but if I do understand what you’re saying, no. You can’t change the CFM of a carburetor. It’s fixed.
In all honesty the only thing I know about a power valve, or rather what I hear, is that a backfire through the intake will kill them. On a side not is it possible to tune a Holley to compare to a Q-Jet in terms of fuel economy?
Mid 90s(?) Holley put a check ball in the base plate to prevent a backfire destroying the PV. Unless it’s a really old carb, it’s likely fine. You’ll know pretty quickly if it isn’t!
Short answer on fuel economy compared to a Qjet is no. There are way more design features on the Qjet to have better economy characteristics. That being said, if economy is really your goal, look to the transmission. You’ll find your biggest gains there. Especially if you’re currently running a 1:1 final drive transmission.
I need that Chev K-20 @ 0:37
That’s my GMC C1500. There’s a couple videos on it. It’s my test mule and cruiser.
I put 780 meatering plates on my 650 carb with a 5 power valve with jets for a 850 carb and I got about 21 miles per gallon of gas as long as I didn't open the 4 bearel but when I stopped the gas pedal it would rip the rear wheels was wicked I still have the car the same engine and the same carb runs awasom
I forgot to mention it was a 289 built
GREAT VIDEO . Thank you for your knowledge and video's USA 🇺🇸 TRUMP