When you have a radical cam you can have a low vacuum situation then the power valves can be opening too soon causing an over rich fuel mixture. Black smoke, (carbon in the tail pipes) a surge and fowled plugs and of course.....terrible fuel economy. A backfire through the carburetor can also rupture the power valve diaphragm. Further info about this is after 1992 to current , Holley added a back fire check valve in the vacuum passage to prevent rupture of the power valve diaphragm . Serious drag racers plug the power valves and increase the jet size at least 6 points higher, Drag racers are not as concerned with fuel economy only ET. Great video .
Dear 1109, Thank you for the kind words. At this time we have not moved into anything regarding adjustable bleeds; we are attempting to cover the essentials for all of our carburetor lines. I hope that as we progress the opportunity to provide additional tuning insights will allow us to cover circuit modifications by using adjustable bleeds. If nothing else, the theory behind this form of tuning will provide additional insight and understanding regarding carburetion.
OK, to answer my own question, I watched a Holley tutorial and the 2:1 thing is the recommended power valve selection. An idle vacuum of 13.0 inches supposedly needs a 13/2 = 6.5 power valve. The 6.5 IS in inches of Mercury.
The logic behind this decision is the similarity in specific gravity, the nature of the petrochemicals and TEL involved in the octane increase; and the general absence of alcohol. Let me share a thought of my own; if in doubt go fatter, add more fuel and pull a little timing out. As you tune and progress you can always bring the timing back in and tune to the proper air-fuel ratio for the fuel being used. I hope this helps; good luck.
If you turn in the mixture screws and the engine stumbles your power valve is NOT blown. If you have both screws ALL THE WAY clockwise and the engines didn't drop RPM's then the power valve needs replaced.
Very important; I will assume that you are carbureted and not EFI. I have not gone the route of avgas and have generally stayed with mogas through the years. Everything I find suggests that your jet sizes will remain essentially where they are at. You might eventually see a 1, 2 or 3% change going leaner from your current jet sizes.
The fact that the carb has sat without fuel for so long means there is a high probability that the gaskets/seals and any rubber components have dried out. Trying to reuse it now without freshening these components will most likely result in leaks and potentially a fire. We highly suggest a rebuild kit and soaking at least overnight in a carb cleaning solution to rid the carb of any varnish that may have built up over the years. Thanks for watching! Good luck :)
I installed a AEM air fuel ratio gauge it came with the weld in bung the muffler shop welded it in right in the header collector so I get all four cylinders with out it I was guessing on jetting / the easiest for me was as he suggested with idle set correct speed with eng at normal temp put it in D read vacum gauge 12 divide that by 2=6... there is no 6 so use 5.5 or whatever your reading is , I have yet to drive with the vacum gauge strapped to the wiper but with PV that is really only way to fine tune it just like a AFR gauge for jetting .
Almost told me what I needed to know. I need to know what power valve size I need for a carb with 2 power valves? One needs to be half and the other a 1/4 of vacuum? I'm not sure how that works.
I have 19.6hg at idle in natural.. And about 15hg in drive. Already had put a 6.5 in there and seems that is what this method would suggest. BUT... The second method suggests a 13 power valve? Do they come bigger then 10.5"? lol I like the 3 cruise speed method. That will put it right where you need it with out any fuss. I'm gonna try that and see what I come up with.
Hi, Wondering what Ur opinion was on cleaning the inside of the carb, short of rebuilding or a refresh kit. I have a Holley 650 double pumper 4777-4. Carb has been sitting like 7 to 8 years, It's empty now. Haven't tried to start engine yet, Wondering if spraying carb cleaner inside Vent tube to mix it with the fresh gas in the bowls while engine is running. Do U think a little bit of cleaner would ruin anything on the inside of carb?
i.m geting 6-8 inches of vacuum at idle(241@50 duration cam,484 lift) ,and i have A 6.5 powervalve,does that mean my powerrvalve is always opened when i,m idling?
Hey Norm, I ordered the pump cam tuning kit from you guys. Im thinking about ordering a power valve kit. I cant seem to get my sbc 350 to come alive with the quick fuel 600vs. It ran fine on a quadajet. but now trying to deal with all this holley stuff. Do you think that buying a holley vs their sub brand of quick fuel would be better?
This is old school bad information. My vacuum is 6 at idle. I have a A/F gauge. Reduced main jets for better gas mileage. Needed power valve to come in earlier, put in a high vacuum PV to overcome lean condition while accelerating. Opened up restrictions in valve body. No affect on idle Air fuel.
I saw a graphic that says that the number stamped on the power valve should be multiplied by two (a 6.5 would actually = 13.0). This implies that the number on the valve must be in psia. Multiplying that number would give you inches of Mercury. Which is correct? one other thing about idle quality and power valves. I'd be quite surprised that an open power valve at idle would have much effect on A/F ratio. 95% of the fuel restriction at idle is the idle mixture screw. I'd think that removing the jets completely wouldn't change the fuel flow appreciably at idle. I tend to think that anybody who changed a power valve and the engine idled much better had a blown power valve.
The number on the valve is when it will open. In your example, a PV stamped 6.5 will open when engine vacuum drops below 6.5" of vacuum. Power valves are typically sized at 1/2 of. engine vacuum. So a 6.5 PV would typically be installed on an engine with 13" of manifold vacuum. You are correct about blown power valve, it will make it nearly impossible to calibrate idle mix screws. When the power valve is open due to failure or low vacuum it allows more fuel into the main jet circuit. The idle circuit shares the same main jet circuit after fuel passes by the mix screws. If the PV is blown it will allow un-metered fuel into the engine at all times. PV has no effect on idle if its not blown. Large vacuum leaks may allow it to open and it its sized lower than engine vacuum at idle it will also open
I have a Lamba sensor and fuel ratio meter, can I therefore obtain a more definite determination of my cars power valve need using this? I am guessing when I am cruising at a vacuum above the power valve number, it is the main jets that determine the mixture, then when I open the throttle to decrease the vacuum to where the power valve opens, I need to then adjust my powervalve to maintain the correct fuel air ratio?
Hi Peter Rossa, The use of a vacuum gauge will certainly help you define the proper opening time of the power valve and at a steady state cruise it should be closed. At this point, info from your wide band O2 sensor will point you in the right direction of proper main jetting. Ultra-fine tuning can also be done by swapping air bleeds in the metering blocks if your carb is equipped that way.
They are totally different. The acc. pump squirts fuel when you open the throttle quick,which richens the sudden rush of air,so that it doesn't stumble. The power valve only kicks in when the vacuum drops and you need a continuous supply of fuel for hauling ass.
Why exactly would you consider either a 5.5 an 8 when the engine is producing 12hg.? I would think the two different spring rates would do two different things. You have not explained that.
Hi, i have a 600 v/s Holley on a 289 with a Comp Thumper Cam and AFR 165 heads (no heat crossover). I have really low manifold vacuum at idle - 5 to 8 deg depending on revs/timing. Is it possible that the standard power valve could be opening at idle? i have adjusted the idle mixture screws to give me the best vacuum i can get (about 1 3/4 turns out) but found raw fuel sitting in the manifold (edelbrock rpm) when i removed the carb. Runs fine out on the open road but idle is all over the place - even for a lumpy cam. Cheers.
***** , Yes, keep in mind that the number stamped on a Holley power valve is the opening point. So, if you have a 6.5” p/v installed now, the unsteady vacuum signal it is seeing is allowing it to open prematurely.
Summit Racing Thanks. I've replaced the Power Valve with a 3.5 and its made a massive difference to the idle quality. Looking forward to applying the rest of the tips from your videos. Great work guys.
okay, I've got a couple of questions I've been searching for answers on. I have a 377ci sbc with a handed down 750 cfm 80508 Holley. 700r4, blah blah blah, tired of typing this stuff for no responces. so I have a major hesitation with quick throttle opening. I have the largest accel pump cam from aed. 1st position. 30cc pump. .035 squirter. may go back down. from holleys original instuctions I've come up with a 7.5 power valve. I've yet to test the vacuum while driving, do to not knowing about that, cause Holley never mentioned it -_- so for many months I be been searching for a damn answer to WHY the hesitation won't go away. I stumble on this video and what do you know? test while driving huh? now, let's see if I can get some gas for my truck since ive been shoving money towards it to try to get it working cause Holley never told me to test the vacuum while driving to determine proper power valve size. thanks summit, this is why I come to you and not the other guys!
Nice video! Please can you tell me what happens if I have a wrong PV that opens too "late" (on too high load)? I have a 4160 probably with a 6,5 PV and the engine is bucking slightly if I leave cruising into a slight acceleration. Und der full load everything is fine. So my assumption is I need a 8,5 or 10,5 PV, correct? Tanks!
Markus Dörschmidt , Keeping in mind that the number printed on the PV is its actual opening point, you could install a vacuum gauge so you could see what the vacuum is doing while driving and make a better choice with less guessing!
Markus Dörschmidt Let me guess, you have a holley street avenger? If so then you'll need to swap metering blocks. The avengers have leaned out transfer circuit. Larger pump nozzle will cover slightly, but not under "slight" peddle movement. If you move quickly past that spot does it do ok? Sounds like you have the same problem I had. Slight peddle shouldn't get in to the power valve yet. Unless you put a 10.5 in or something. I hit 6.5hg at about 3/4 primary opening. Get on ebay and get some of the billet metering blocks specifically for your carb size. Quick Fuel makes them calibrated for cfm. That should solve the stumble at slight throttle move from cruise. Then run a vacuum line in side and use the vacuum gauge described in video. If you really want to know what is going on with your carb and it's fuel supply get a wide band o2 and A/F gauge. Thats what I did. I can see exactly what my accelerator pump, power valve and jets are doing. If there is a lean spot you see what Vacuum it occures at and put that size power valve in. Or you'll see if it's the accel. pump shot that needs adjusting. Once the pump shot is tuned, and power valve then you can hold primarys wide open (secondarys shut) and tune jets based on air fuel readings. Your power valve will pick up where accel shot leaves off and then overlap on top of the jets when they catch up.
Thoroughly convoluted power valve. A power valve should be closed at idle, using the idle jets only, as the first or primary butterfly opens the power valve will also open, lower vacuum, based on the power valve vacuum setting such as 4.5, 5.5, 6.5, etc, this will increase the fuel flow, The jets are fixed in size, the power valve will have low flow or high flow depending which type of power valve you have. The power valve is really just a type of vacuum setting, opening or closing, there is no metering at all, open, close thats it. Holley is good for performance, not so good for gas mileage. For gas mileage use a Carter / Edelbrock carburetor or an old Rochester carburetor, they're old, but work good.
Thanks Norm for the great explanations. By the way I m Norm as well. I have a mild 302 in my '65 Mustang with the Holley 4160 I think. Has the standard 6.5PV. I have a steady 20" in park and 15.5" in drive. I do sometimes get a bad hesitation like the engine cuts out only when the RPMs are low at low speed and I gently press the gas. If I press harder it surges and runs good. Not taken the cruising vacuum reading yet but I will. Based on this video does it make sense that I need a high number PV? Sounds like one between 7.5PV - 12PV. Think to split the middle and try a 10.5PV? Thoughts?
Hi Norm, From what I can tell it looks like the 6.5 is very close; since you are at 15.5 inches in gear you might elect to try the 7.5 inch valve. Nutshell: Automatic transmission @ operating temperature, in gear, use ½ of vacuum reading and go down to nearest size. In this instance, 7.5. Norm, your hesitation sounds like accelerator pump circuit from what I read. Best.
+Summit Racing Thanks Norm. I tried the 10.5 PV and the car was nearly underivable; put back the 6.5 PV. Eventually I will try the 7.5 PV. I've been changing the accelerator circuit to eliminate the just off idle hesitation that seems like the engine turns off. I upped the nozzle from a 31 to a 35 which helped but still has the problem.
@@normcoffey4296 I have 15" at cruise and 5" at idle. The stock pv was 6.5". It was ok. I then tried a 8.5". At cruise, it was ok (I have a afr gauge), but when taking off from a stop sign with light throttle, the valve opens up below 8.5" (no load, no real rpm), and it dumps the fuel in. It went way rich (10:1 afr, with no load is no good!) Hell, I'm aiming for 13:1 afr at wot, full load! I switched to a 4.5" and it's fine. When I cruise and then get on it, the Vac goes from 15" to 1" in a split second. Power valve still opens in 0.15 seconds, no sweat, and I'm not dumping fuel just to get rolling with 4.11 gears!
When you have a racing profile cam in your car it can miss fire just slightly off Idle like in a normal driving condition if you have the incorrect power valve . Too much fuel at this lower RPM will blacken your tailpipes and foul your spark plugs . You all have smelled exactly what I am talking about here.
Hi Chase Reynolds, A bad power valve will cause higher fuel consumption, black smoke out the tailpipe and usually the engine will be less responsive, meaning it may bog or hesitate off of idle.
Might be the best power valve video I’ve seen so far, thanks for the info Norm!
I agree.
I am really enjoying this whole series on holley carbs and I'm learning a ton. I can't wait for more!
When you have a radical cam you can have a low vacuum situation then the power valves can be opening too soon causing an
over rich fuel mixture. Black smoke, (carbon in the tail pipes) a surge and fowled plugs and of course.....terrible fuel economy. A backfire through the carburetor can also rupture the power valve diaphragm. Further info about this is after 1992 to current ,
Holley added a back fire check valve in the vacuum passage to prevent rupture of the
power valve diaphragm . Serious drag racers plug the power valves and increase the jet size at least 6 points higher, Drag racers are not as concerned with fuel economy only ET. Great video .
This a great video and Norm is an outstanding narrator; clear and concise.
Thank you, Mikey Asmus! Let us know if you have any questions.
Thank you, Ron!
Dear 1109,
Thank you for the kind words. At this time we have not moved into anything regarding adjustable bleeds; we are attempting to cover the essentials for all of our carburetor lines. I hope that as we progress the opportunity to provide additional tuning insights will allow us to cover circuit modifications by using adjustable bleeds. If nothing else, the theory behind this form of tuning will provide additional insight and understanding regarding carburetion.
OK, to answer my own question, I watched a Holley tutorial and the 2:1 thing is the recommended power valve selection. An idle vacuum of 13.0 inches supposedly needs a 13/2 = 6.5 power valve. The 6.5 IS in inches of Mercury.
The logic behind this decision is the similarity in specific gravity, the nature of the petrochemicals and TEL involved in the octane increase; and the general absence of alcohol.
Let me share a thought of my own; if in doubt go fatter, add more fuel and pull a little timing out. As you tune and progress you can always bring the timing back in and tune to the proper air-fuel ratio for the fuel being used.
I hope this helps; good luck.
You are a pro at explaining things!
Excellent tutorial,Norm
Thank you for watching, Steven!
I wish you were my next door neighbour..
If you turn in the mixture screws and the engine stumbles your power valve is NOT blown. If you have both screws ALL THE WAY clockwise and the engines didn't drop RPM's then the power valve needs replaced.
You just saved hours of my life thank you
Does that work on a large carburetor with for mixture screws two on the primary and two on the secondary
Very important; I will assume that you are carbureted and not EFI. I have not gone the route of avgas and have generally stayed with mogas through the years. Everything I find suggests that your jet sizes will remain essentially where they are at. You might eventually see a 1, 2 or 3% change going leaner from your current jet sizes.
The fact that the carb has sat without fuel for so long means there is a high probability that the gaskets/seals and any rubber components have dried out. Trying to reuse it now without freshening these components will most likely result in leaks and potentially a fire. We highly suggest a rebuild kit and soaking at least overnight in a carb cleaning solution to rid the carb of any varnish that may have built up over the years. Thanks for watching! Good luck :)
Please continue to call them like you see them; if there is something I have missed or gone astray on please let me know. Thank you.
I installed a AEM air fuel ratio gauge it came with the weld in bung the muffler shop welded it in right in the header collector so I get all four cylinders with out it I was guessing on jetting / the easiest for me was as he suggested with idle set correct speed with eng at normal temp put it in D read vacum gauge 12 divide that by 2=6... there is no 6 so use 5.5 or whatever your reading is , I have yet to drive with the vacum gauge strapped to the wiper but with PV that is really only way to fine tune it just like a AFR gauge for jetting .
Sure makes switching to throttle body fuel injection seem awesome!
Top job Norm, very informative. Have you done any videos on the screw in air bleeds for the Idle and Main circuits yet? Cheers Rick from OZ.....
Almost told me what I needed to know. I need to know what power valve size I need for a carb with 2 power valves? One needs to be half and the other a 1/4 of vacuum? I'm not sure how that works.
I have 19.6hg at idle in natural.. And about 15hg in drive. Already had put a 6.5 in there and seems that is what this method would suggest. BUT... The second method suggests a 13 power valve? Do they come bigger then 10.5"? lol
I like the 3 cruise speed method. That will put it right where you need it with out any fuss. I'm gonna try that and see what I come up with.
Dave S,
Can you give our tech line a call? 1-330-630-0240. We need some additional information from you. Thanks!
I have motorcraft Holley 4180 what I like to know is what size of power valve I can put in since is a two stage
Where's the Holley Ultra Dominator for these videos, they have more adjustments than you can shake a stick at ?
How do I know what valve do I need for my 5.8 liter for? I have a Holley 4bbl carburetor.
Hi, Wondering what Ur opinion was on cleaning the inside of the carb, short of rebuilding or a refresh kit. I have a Holley 650 double pumper 4777-4. Carb has been sitting like 7 to 8 years, It's empty now. Haven't tried to start engine yet, Wondering if spraying carb cleaner inside Vent tube to mix it with the fresh gas in the bowls while engine is running. Do U think a little bit of cleaner would ruin anything on the inside of carb?
Why have I also heard to choose a power valve PV which opens 1-1/2" to 2" Hg below the minimum steady vacuum reading. Which one the best way?
i.m geting 6-8 inches of vacuum at idle(241@50 duration cam,484 lift) ,and i have A 6.5 powervalve,does that mean my powerrvalve is always opened when i,m idling?
Hey Norm, I ordered the pump cam tuning kit from you guys. Im thinking about ordering a power valve kit. I cant seem to get my sbc 350 to come alive with the quick fuel 600vs. It ran fine on a quadajet. but now trying to deal with all this holley stuff. Do you think that buying a holley vs their sub brand of quick fuel would be better?
This is old school bad information.
My vacuum is 6 at idle.
I have a A/F gauge. Reduced main jets for better gas mileage. Needed power valve to come in earlier, put in a high vacuum PV to overcome lean condition while accelerating. Opened up restrictions in valve body.
No affect on idle Air fuel.
I saw a graphic that says that the number stamped on the power valve should be multiplied by two (a 6.5 would actually = 13.0). This implies that the number on the valve must be in psia. Multiplying that number would give you inches of Mercury. Which is correct? one other thing about idle quality and power valves. I'd be quite surprised that an open power valve at idle would have much effect on A/F ratio. 95% of the fuel restriction at idle is the idle mixture screw. I'd think that removing the jets completely wouldn't change the fuel flow appreciably at idle. I tend to think that anybody who changed a power valve and the engine idled much better had a blown power valve.
Hi Ken B,
We have some options for you but we need some additional information. Can you please give us a call 1-330-630-0240.
Com
The number on the valve is when it will open. In your example, a PV stamped 6.5 will open when engine vacuum drops below 6.5" of vacuum. Power valves are typically sized at 1/2 of. engine vacuum. So a 6.5 PV would typically be installed on an engine with 13" of manifold vacuum. You are correct about blown power valve, it will make it nearly impossible to calibrate idle mix screws. When the power valve is open due to failure or low vacuum it allows more fuel into the main jet circuit. The idle circuit shares the same main jet circuit after fuel passes by the mix screws. If the PV is blown it will allow un-metered fuel into the engine at all times. PV has no effect on idle if its not blown. Large vacuum leaks may allow it to open and it its sized lower than engine vacuum at idle it will also open
hey summit racing , i was wondering if a f150 2003 4.2 v6 can be converted into a posi trac.
Does Summit Racing Quick Flicks have any videos on Rochester Quadra-Jet carb tech/rebuilding.
Love these videos! Great info
Thank you for watching, Matthew!
Very Very informative. Great job. This helped me so much. Thank you.
Hi SickSilverado1982,
Thank you! Let us know if you have any questions.
I have a Lamba sensor and fuel ratio meter, can I therefore obtain a more definite determination of my cars power valve need using this? I am guessing when I am cruising at a vacuum above the power valve number, it is the main jets that determine the mixture, then when I open the throttle to decrease the vacuum to where the power valve opens, I need to then adjust my powervalve to maintain the correct fuel air ratio?
Hi Peter Rossa,
The use of a vacuum gauge will certainly help you define the proper opening time of the power valve and at a steady state cruise it should be closed. At this point, info from your wide band O2 sensor will point you in the right direction of proper main jetting. Ultra-fine tuning can also be done by swapping air bleeds in the metering blocks if your carb is equipped that way.
The racers with Dominators do this but you shouldn't go too far without the instruments. Excellent video.
so how is the Power Valve different from the Accelerator Pump? both enrich the fuel mixture, why have both and not either or
They are totally different. The acc. pump squirts fuel when you open the throttle quick,which richens the sudden rush of air,so that it doesn't stumble. The power valve only kicks in when the vacuum drops and you need a continuous supply of fuel for hauling ass.
Why exactly would you consider either a 5.5 an 8 when the engine is producing 12hg.? I would think the two different spring rates would do two different things. You have not explained that.
Hi, i have a 600 v/s Holley on a 289 with a Comp Thumper Cam and AFR 165 heads (no heat crossover). I have really low manifold vacuum at idle - 5 to 8 deg depending on revs/timing. Is it possible that the standard power valve could be opening at idle? i have adjusted the idle mixture screws to give me the best vacuum i can get (about 1 3/4 turns out) but found raw fuel sitting in the manifold (edelbrock rpm) when i removed the carb. Runs fine out on the open road but idle is all over the place - even for a lumpy cam. Cheers.
***** ,
Yes, keep in mind that the number stamped on a Holley power valve is the opening point. So, if you have a 6.5” p/v installed now, the unsteady vacuum signal it is seeing is allowing it to open prematurely.
Summit Racing Thanks. I've replaced the Power Valve with a 3.5 and its made a massive difference to the idle quality. Looking forward to applying the rest of the tips from your videos. Great work guys.
I was going to try that if the carb didn't run right before trying to rebuild it.
okay, I've got a couple of questions I've been searching for answers on.
I have a 377ci sbc with a handed down 750 cfm 80508 Holley.
700r4, blah blah blah, tired of typing this stuff for no responces.
so I have a major hesitation with quick throttle opening. I have the largest accel pump cam from aed. 1st position.
30cc pump. .035 squirter. may go back down.
from holleys original instuctions I've come up with a 7.5 power valve. I've yet to test the vacuum while driving, do to not knowing about that, cause Holley never mentioned it -_-
so for many months I be been searching for a damn answer to WHY the hesitation won't go away. I stumble on this video and what do you know? test while driving huh? now, let's see if I can get some gas for my truck since ive been shoving money towards it to try to get it working cause Holley never told me to test the vacuum while driving to determine proper power valve size. thanks summit, this is why I come to you and not the other guys!
Nice video!
Please can you tell me what happens if I have a wrong PV that opens too "late" (on too high load)?
I have a 4160 probably with a 6,5 PV and the engine is bucking slightly if I leave cruising into a slight acceleration. Und der full load everything is fine.
So my assumption is I need a 8,5 or 10,5 PV, correct?
Tanks!
Markus Dörschmidt ,
Keeping in mind that the number printed on the PV is its actual opening point, you could install a vacuum gauge so you could see what the vacuum is doing while driving and make a better choice with less guessing!
Markus Dörschmidt Let me guess, you have a holley street avenger? If so then you'll need to swap metering blocks. The avengers have leaned out transfer circuit. Larger pump nozzle will cover slightly, but not under "slight" peddle movement. If you move quickly past that spot does it do ok? Sounds like you have the same problem I had. Slight peddle shouldn't get in to the power valve yet. Unless you put a 10.5 in or something. I hit 6.5hg at about 3/4 primary opening.
Get on ebay and get some of the billet metering blocks specifically for your carb size. Quick Fuel makes them calibrated for cfm. That should solve the stumble at slight throttle move from cruise. Then run a vacuum line in side and use the vacuum gauge described in video.
If you really want to know what is going on with your carb and it's fuel supply get a wide band o2 and A/F gauge. Thats what I did. I can see exactly what my accelerator pump, power valve and jets are doing. If there is a lean spot you see what Vacuum it occures at and put that size power valve in. Or you'll see if it's the accel. pump shot that needs adjusting.
Once the pump shot is tuned, and power valve then you can hold primarys wide open (secondarys shut) and tune jets based on air fuel readings. Your power valve will pick up where accel shot leaves off and then overlap on top of the jets when they catch up.
Thank you for watching! We appreciate the feedback. Please let us know if you have any video suggestions.
Thoroughly convoluted power valve. A power valve should be closed at idle, using the idle jets only, as the first or primary butterfly opens the power valve will also open, lower vacuum, based on the power valve vacuum setting such as 4.5, 5.5, 6.5, etc, this will increase the fuel flow, The jets are fixed in size, the power valve will have low flow or high flow depending which type of power valve you have. The power valve is really just a type of vacuum setting, opening or closing, there is no metering at all, open, close thats it. Holley is good for performance, not so good for gas mileage. For gas mileage use a Carter / Edelbrock carburetor or an old Rochester carburetor, they're old, but work good.
why all that bunch off carburetors in that little table?,it make me nervous ,it make you look like not have room for move
It sure can. Give us a call and we can compile a parts list for you and give you some pointers on installation! 1-330-630-0240
Thanks Norm for the great explanations. By the way I m Norm as well. I have a mild 302 in my '65 Mustang with the Holley 4160 I think. Has the standard 6.5PV. I have a steady 20" in park and 15.5" in drive. I do sometimes get a bad hesitation like the engine cuts out only when the RPMs are low at low speed and I gently press the gas. If I press harder it surges and runs good. Not taken the cruising vacuum reading yet but I will. Based on this video does it make sense that I need a high number PV? Sounds like one between 7.5PV - 12PV. Think to split the middle and try a 10.5PV? Thoughts?
Hi Norm,
From what I can tell it looks like the 6.5 is very close; since you are at 15.5 inches in gear you might elect to try the 7.5 inch valve.
Nutshell: Automatic transmission @ operating temperature, in gear, use ½ of vacuum reading and go down to nearest size. In this instance, 7.5.
Norm, your hesitation sounds like accelerator pump circuit from what I read.
Best.
+Summit Racing Thanks Norm. I tried the 10.5 PV and the car was nearly underivable; put back the 6.5 PV. Eventually I will try the 7.5 PV. I've been changing the accelerator circuit to eliminate the just off idle hesitation that seems like the engine turns off. I upped the nozzle from a 31 to a 35 which helped but still has the problem.
@@normcoffey4296 I have 15" at cruise and 5" at idle. The stock pv was 6.5". It was ok. I then tried a 8.5". At cruise, it was ok (I have a afr gauge), but when taking off from a stop sign with light throttle, the valve opens up below 8.5" (no load, no real rpm), and it dumps the fuel in. It went way rich (10:1 afr, with no load is no good!)
Hell, I'm aiming for 13:1 afr at wot, full load!
I switched to a 4.5" and it's fine.
When I cruise and then get on it, the Vac goes from 15" to 1" in a split second. Power valve still opens in 0.15 seconds, no sweat, and I'm not dumping fuel just to get rolling with 4.11 gears!
When you have a racing profile cam in your car it can miss fire just slightly off Idle like in a normal driving
condition if you have the incorrect power valve . Too much fuel at this lower RPM will blacken your tailpipes and foul
your spark plugs . You all have smelled exactly what I am talking about here.
what would be a sign that the power valve is bad
Hi Chase Reynolds,
A bad power valve will cause higher fuel consumption, black smoke out the tailpipe and usually the engine will be less responsive, meaning it may bog or hesitate off of idle.
Black plugs smoke ,real rich
Ok?...Ok
I think he over-explains everything.
+dfinkie me,
We appreciate your input! Thanks for watching. :)
Please quit smacking your lips ! My lady friend just ran out of the room because of this...STOP IT NOW !
You probably should watch your self to see just how many times you say "OK". Too many for me to last to the end.
this is terrible