Paul, 25 year dyno guy here. 1) megaphone pipes and/or long duration cams will lead dyno sniffers into the weeds 2) I remember thinking in a previous video that something was not right with that choke delete. But I don’t know what it was. 3) throw a Keihin FCR on the thing, they are so easy to tune! 😀
@@paulbrodiedo you have something like a separate channel only for the idle, like in a car carburettor? The one that you set with a screew? Because if not then it's next to impossible to set the idle right by leaving the throttle a little open. Can't wait to the next video!
Jetting can be a real pain, but no doubt you’ll figure it out. I ride a 70 bmw r50/5 and have two carbs to deal with and no vacuum port so I understand😊
When I tuned my drz400 I installed a wideband and learned quite a few things. All the recommended needles worked great off idle and wide open, but were stupid rich at cruise. Once I found a needle that got cruise leaned out I ended up larger on the main to compensate for the different needle and position. I also learned the 3x3 hole in the airbox was not nearly enough, now my airbox is basically non existant, but it runs clean everywhere. It's a real rabbit hole to get jetting to all work together.
Paul, two publications which may help are 'The Carburettor Manual' and 'Choosing and Adjusting Slide Carburettors', both published by Dell 'Orto. Your Dell 'Orto dealer should be able to get them. Here in England, it is Eurocarb. They are invaluable for working out what is going on at any given throttle opening. Best wishes, Dean.
In my 70s and still learning . The best motorcycle mechanic I ever knew passed away suddenly of Heart failure a really wonderful guy always willing to help . Now I'm on my own ,He really left a lot of parts and the like behind . His son is going to carry on but lives in Alaska . Thanks Paul for the interesting content , have not turned in for a bit .
A bunch of years ago, I built a BSA 441 into a 500cc and got a cam from Norris Camahaft Grinders (I believe they are defunct for some time). I adapted Chrysler electronic ignition, left the centrifugal advance. I cut the off the distributor cam and brazed the reluctor onto the shaft to keep it from turnig. I also used an automobile coil instead of a Lucas. I could not afford Joe Hunt magneto What I am getting at is I purchased a Lectron flat slide carburetor about 2 or 4 mm larger (forgot which) than the stock Amal. That bike never skipped a beat with that carb. It didn't matter what the throttle opening was, twisting it open produced honest acceleration to top end. It never fouled a spark plug and it burned clean. You can only raise or lower the needle to alter jetting in the Lectron. I have seen then from time to time on E bay but I am not in the market to purchase any so they are rare today. Mikuni won out globally. Good luck with getting the carb dialed in. You may have to go to a Mikuni but knowing you from the videos, I bet you will get it working good. Good Luck at the salt flats. Have Mitch record everything dealing with the inspection to every race and what had to be done in between. It will be a great series of videos.
Every one thinks a few mods, a noisy exhaust, a dynojet kit (modernish bikes only!) and voila, a power increase to compete on the grid at Moto GP! As a builder of bikes among my engineering activities, tuning a self made race bike is a thoroughly long task! Good luck Paul! great build
high paul i notice your using an amal mk2 ,i had similar issues whilst testing on the dyno try checking the float height ,if its low it will cause the bike to run lean ,if this is the case it can be altered by pressing the valve float seat deeper in to the float bowl also make shore your ignition timing is right before you try adjusting your carb settings ,good luck from an old bike racer. p.s if you require any parts for your carb let me know and i will send them to you
finally .. the ermaky gets a chance to roar !! ... and I suggest to try a steel and cotton combo air filter .. it may help with the ventury action in the mid range by sucking more fuel with the help of the increased vacume in the carb without the need to further enlarge the main jet .. the 350 will do in conjunction with a "low obstruction " air filter ... great video .. hope it helps ..
That day at the Dyno was very frustrating, but I went back a week later after making a LOT of changes, and then had a Big smile on my face! Next video I will explain...
I like how Dave apologizes. 😂 Very interesting to see how this process plays out in real life. It will go better next time with all the data you’ve collected. Cheers!
Back in the 80's I made a manifold adapter to run a Zenith Stromberg (think it came off a Volvo) on my Harley. So tuning issues was to get the correct taper on the needle. I made a chart, measured the diameter every 1/10 inch (.100") with a micrometer. Then I made charts to show different rates of taper at every 1/10". I used Amal needles and fine filed them to size in my drill press, sanded them down to a 600 sand paper. I then had to sleeve the top of them to hold them in the slide. The second needle worked the best , spot on from idle, midrange, and full throttle. Interesting, the difference at 1,500" to sea level was just 1/2 turn more open of the main jet. At sea level the clutch would slip, but not at 1,500'. You could also raise your needle by making small washers under it in the slide too.
You need to get close on the main jet first for your WOT operation and then clean up the mid range. Float level check needs done before any tuning. Also try tuning without the velocity stack on the carb , I have had problems with them effecting carburetor operation and needed to find a different style of stack. Tune for the task, WOT in your case, you don't need to worry about response coming out of the turn.😀
Definitely seems mid range / needle related. Since it's running lean at mid throttle with the needle in the top position, a thinner needle may be what it needs. Jetting is a bit of a black art.
If that's Mikuni carb the number stamped on the jet is not a drill size for the hole through it, Mikuni do a chart to interpret the drill size of your jet from the number stamped on it, bear in mind that with Mikuni carbs the drill size is always a lot smaller than the jet number. Your issue with lean running is more likely down to the needle and atomiser combination, by all means shave down your existing needle which will richen it up but, do it progressively and test each time you file/shave the needle to check out the effect. Roland, HT Racing Ltd
Hi Paul, roughly speaking from quarter to three quarter throttle is all needle jet and not main jet. I also agree with Paul the dyno guy, unless the formula demands the original Amal carby put a Keihin on it or even a mikuni if you can’t stretch to the Keihin.
You may look at the ignition pattern also. Maybe you are not getting the advance quite correct in the mid range which is hurting the high end pull. Good luck at the slat flats. Keep it straight on the black line. That's right they don't use the black line now.
Ah the adventure that is jetting a custom motorcycle. One step forwards and two steps backwards. Paul, I am sure you will be getting lots of suggestions on the direction of your jetting, but in all the conversations from main jet to needle and needle jet and pipe configuration nobody mentioned the slide cutaway. You have a lean condition in the mid-range, so some careful filing of the slide could help you. I am stunned that as a man who never throws anything away, that you don't have your original jetting specs from your old 350. Good luck, I am sure you will work it out.
@@vintagebike_ger ...my apologies. I actually woke up during the night and wondered what the hell had I said in my response to Pauls video. Thanks for correcting my error... 🙂
Friend of mine spent several years running dyno in Belgium, (former US Marine, met guy while training after service ) He told me they spent a lot of time setting airflow in the 'dyno room' to get closer to 'real world conditions' as if bikes were on the street at 100mph (or maybe 100KPH? I forget) Guess I should get in touch with him as he's on Facebook. Even though I watched the 'new' video first, it sounds like mid range is the issue which can be adjusted by needle taper. (only tried making a carb needle once, way too difficult but modifying is quite easy) I should probably watch video before commenting instead of stopping when I think of something Short pipes will get best top end power but over a narrow rpm range and are a bear to tune for at lower rpm, (it's been 'quite well known' since Manx Norton in 1950's with 'megaphonitis') Usual sidetrack, a Harley Sportster 883 with 'drag pipes' actually loses at least 4bhp as pipes are tuned length for a ~ 8,500 - 9,000 rpm motor. Even after extensive dyno tuning they only get back to stock power output ( before setting up make about 40~44 bhp, well, in early 2000's) Is that Mustang Dynamometer from Australia? k I have read good things about them.
Disappointing but that is what is so good with a Dyno session. I guess it one step forward and two steps back, but I know you'll sort it out. I also have to say that the bike looks great.
If that Tech said it would run better without the piston, I’d listen to him.
3 หลายเดือนก่อน
That’s Amal Mk2 have one in my BSA Gold Star. 2 things to check. You may need a deeper float and also the position of the pilot jet - 2 positions try both.
I had a lean midrange on a Husky 430 CR that could only be corrected with a different slide. No amount of main jet or needle adjustment would correct it. Mikuni carb. Good luck.
Do you maybe have an air leak? Like a throttle shaft that is worn, letting unmetered air in? That would show up as a lean mixture at idle, correcting at higher RPMs. A fresh needle may be in order as well, they'll wear against the inner bore of the jet, screwing up the taper.
Main jet only affects the top end. You could plug it and it would still run. You probably need to get a richer needle. You could have tried shimming the needle, that might have worked.
Some of those "Runs" sounded ignition related to me, but I'm not an Aermacchi guy, I own all Ancient Ducati singles - You might try and whole different carb, ie- more modern, I've seen a lot of fellas with good results from the new flatslides than trying to mess around with old-worn finicky Dellorto or Amal junk? I dont envy your situation
I can't help but be remembered the one night we had a ignition condenser in the distributor go bad in our race car. It started to run very rough in the mid-range and just wouldn't get out of the bogging mid rpm's. This continued for maybe 20-30 minutes of trying to trouble shoot until we eventually just lost all spark. Changed the condenser for one we snatched from the old water truck, and everything was fixed! I guessed the condenser developed a crack or a point that limited its capacity and over the short time just failed. But then i have seen motors that had the distributor shaft with the mechanical/vacuum advance freeze in place and do something similar with having poor midrange fuel ignition.
I am nt sure what you want from the bike. If its for flat out speed runs then its important to get wide open throttle power. If it is to be used on the road then idle and low end (part throttle) performance is the most important. I normally mess with cars and I have often seen people try to put carbs that are too large on their engines. This leads to slow airflow through the carb and makes it have poor response for the engine. High HC readings at idle usually mean that the engine is missing.
Why would you be drilling out the main jet when it’s the midrange that’s rich? Should you not be looking at the needle jet and the jet needle in that range? Take the main jet out completely and run the bike. It should flood when opened fully but it should still be lean in the midrange.
I only had a couple of needle jets, and two needles... However, I did get it figured out, and I'll talk all about that next video. It was a big learning curve for me...
I would think if you were thinking it was running on the choke it would be coming out the bottom of the bowl its jetted wrong to maybe the airbox or whatever stock air box or you remove the air box?
As others have said, attention to the main jet size was a mistake, as that is only critical at full bore. It may be worth experimenting with different size slide cutaways? I believe that the ones made for the AMAL mk1 fit as well, or is your mk2 a smooth bore? Frustrating when everything else is sorted.
I guess this is where everyone puts in their two cents. Seems like the carb is so far off, I'd see if I could get it working with a K&N air filter installed and then after that see what it does with only the velocity stack. Otherwise you may just end up tuning for top end and sacrificing drive-ability.
The idle "4 stroking" is likely too rich at idle, falling on its face when opening the throttle is a too lean midrange and is usually needle related, the clip should be lowered thereby raising the needle out of the jet some. The main jet is is usually only applicable at wide open. On an Amal the slide cutaway and needle are responsible for midrange (some would argue for emulsion tube involvement also). Dellortos are a different beast but may be similar. You could scan "Bushman's carb tuning secrets" for better information than I've got.
Mmmm, sounds like the main is too large but the needle taper and the cutout are incorrect. Carb being too large tends to make jetting difficult. Needs to develop air velocity to draw fuel and the stumble as at partial throttle. Idle is idle, cutout has a big part til above 1/3 throttle, needle controls the wet side until it's all the way out of the metering housing only then are you fully on the main jet. Another area to double check is float level and that the float valve and supply can deliver. Too rich at full throttle says there's enough for now. Covering the carb with a hand is needle and carb size. Start with needle but consider sourcing something slightly smaller as a backup. IMO
Interesting. but wow, that thing sounded terrible. Could it be something goofy like the cam is off 20 degrees? or some serious voodoo wrong with the ignition module? Best of luck figuring it out.
If the bike is rich wide open, then it is the main jet that is too big. If it's weak at 1/4 to 3/4 throttle then it is the needle & needle jet that is too small. There are not too many options with needle jets & needles on an Amal. Something else is wrong there.
Cannot watch the video, and you are experienced. Another TH-camr was racing in Utah and it got wet, but he was too lazy to clean his vehicle. A lot of parts were unusable when he had time to clean. Interesting how quick that happens.
It really sounded like the carb had an internal leak somewhere.. maybe even float level. Especially since the jetting wasn't really doing a whole lot. She sounded like an absolute weapon though! good work.
man that sucks you didnt get a clean pull, the bike looks great though. im not as learned as you on these bikes but im definitely suspicious of either that carb or the ignition.
I would think if you were thinking it was running on the choke it would be coming out the bottom of the bowl its jetted wrong to maybe the airbox or whatever stock air box or you remove the air box?
Paul, 25 year dyno guy here. 1) megaphone pipes and/or long duration cams will lead dyno sniffers into the weeds 2) I remember thinking in a previous video that something was not right with that choke delete. But I don’t know what it was. 3) throw a Keihin FCR on the thing, they are so easy to tune! 😀
I made a Lot of changes, and went back to the Dyno.. Now it runs very well, but does not idle. I will explain what I went through next video...
@@paulbrodiedo you have something like a separate channel only for the idle, like in a car carburettor? The one that you set with a screew? Because if not then it's next to impossible to set the idle right by leaving the throttle a little open. Can't wait to the next video!
Jetting can be a real pain, but no doubt you’ll figure it out. I ride a 70 bmw r50/5 and have two carbs to deal with and no vacuum port so I understand😊
👍😎👍
Rick, True words. But, I did get it figured out, and that will be our next video, when Mitch turns from Holiday.. Thanks for watching...
When I tuned my drz400 I installed a wideband and learned quite a few things. All the recommended needles worked great off idle and wide open, but were stupid rich at cruise. Once I found a needle that got cruise leaned out I ended up larger on the main to compensate for the different needle and position. I also learned the 3x3 hole in the airbox was not nearly enough, now my airbox is basically non existant, but it runs clean everywhere. It's a real rabbit hole to get jetting to all work together.
ah i miss my old drz, loved that bike.
Yes, tuning a carb for a race motor is not easy...
Great video showing the struggles of a build.
All the best Paul!
Thanks Grant, building a custom race bike is not always easy. Thanks for watching...
Watching your face while you were lettin' 'er rip on the Dyno was priceless 👍👍
Thanks David. I left the Dyno feeling pretty disappointed...
@@paulbrodieyou'll get it, we'll be grinning like fools too. Love this project bike.
Paul, two publications which may help are 'The Carburettor Manual' and 'Choosing and Adjusting Slide Carburettors', both published by Dell 'Orto. Your Dell 'Orto dealer should be able to get them. Here in England, it is Eurocarb.
They are invaluable for working out what is going on at any given throttle opening.
Best wishes, Dean.
Thanks Dean, I did get it figured out. Next video I will do a bit of explaining...
In my 70s and still learning . The best motorcycle mechanic I ever knew passed away suddenly of Heart failure a really wonderful guy always willing to help . Now I'm on my own ,He really left a lot of parts and the like behind . His son is going to carry on but lives in Alaska . Thanks Paul for the interesting content , have not turned in for a bit .
Thanks for watching and commenting...
Carburettors are great... I do love the purely mechanical aspect of them though.
Great video, thanks for sharing. That bike sounds wicked mean. None of my Harley Sprints ever sounded that robust. 👍
Thanks. I did get it figured out... I will explain a lot next video...
Maybe Paul should sell CDs of that sound as a side project, lol. That snappy song is impressive.
A bunch of years ago, I built a BSA 441 into a 500cc and got a cam from Norris Camahaft Grinders (I believe they are defunct for some time). I adapted Chrysler electronic ignition, left the centrifugal advance. I cut the off the distributor cam and brazed the reluctor onto the shaft to keep it from turnig. I also used an automobile coil instead of a Lucas. I could not afford Joe Hunt magneto What I am getting at is I purchased a Lectron flat slide carburetor about 2 or 4 mm larger (forgot which) than the stock Amal. That bike never skipped a beat with that carb. It didn't matter what the throttle opening was, twisting it open produced honest acceleration to top end. It never fouled a spark plug and it burned clean. You can only raise or lower the needle to alter jetting in the Lectron. I have seen then from time to time on E bay but I am not in the market to purchase any so they are rare today. Mikuni won out globally. Good luck with getting the carb dialed in. You may have to go to a Mikuni but knowing you from the videos, I bet you will get it working good. Good Luck at the salt flats. Have Mitch record everything dealing with the inspection to every race and what had to be done in between. It will be a great series of videos.
Every one thinks a few mods, a noisy exhaust, a dynojet kit (modernish bikes only!) and voila, a power increase to compete on the grid at Moto GP! As a builder of bikes among my engineering activities, tuning a self made race bike is a thoroughly long task! Good luck Paul! great build
high paul i notice your using an amal mk2 ,i had similar issues whilst testing on the dyno try checking the float height ,if its low it will cause the bike to run lean ,if this is the case it can be altered by pressing the valve float seat deeper in to the float bowl also make shore your ignition timing is right before you try adjusting your carb settings ,good luck from an old bike racer. p.s if you require any parts for your carb let me know and i will send them to you
Dave 2 sounds like he's an Ulsterman. 🤔
I believe that Dave 2 is a Kiwi...
@@paulbrodieAsk him next time you're up. Had another listen to his accent and my money's on Northern Ireland.
On the plus side she sounds Fookin Awesome! TFS, GB :)
finally .. the ermaky gets a chance to roar !! ... and I suggest to try a steel and cotton combo air filter .. it may help with the ventury action in the mid range by sucking more fuel with the help of the increased vacume in the carb without the need to further enlarge the main jet .. the 350 will do in conjunction with a "low obstruction " air filter ... great video .. hope it helps ..
Sounds deep & wonderful. Especially for a small displacement. Props.
dyno's a such a great tool, but they can be a real pain in the ass too, glad you got a god one operated by a guy who knows his stuff.
That day at the Dyno was very frustrating, but I went back a week later after making a LOT of changes, and then had a Big smile on my face! Next video I will explain...
I like how Dave apologizes. 😂 Very interesting to see how this process plays out in real life. It will go better next time with all the data you’ve collected. Cheers!
Yes, I did get it figured out, and made a Lot of changes.. Next video!!!
Back in the 80's I made a manifold adapter to run a Zenith Stromberg (think it came off a Volvo) on my Harley. So tuning issues was to get the correct taper on the needle. I made a chart, measured the diameter every 1/10 inch (.100") with a micrometer. Then I made charts to show different rates of taper at every 1/10". I used Amal needles and fine filed them to size in my drill press, sanded them down to a 600 sand paper. I then had to sleeve the top of them to hold them in the slide. The second needle worked the best , spot on from idle, midrange, and full throttle. Interesting, the difference at 1,500" to sea level was just 1/2 turn more open of the main jet. At sea level the clutch would slip, but not at 1,500'. You could also raise your needle by making small washers under it in the slide too.
Ive used shim washers quite a bit back preretirement, believe I used to get them from motion pro.
You need to get close on the main jet first for your WOT operation and then clean up the mid range. Float level check needs done before any tuning. Also try tuning without the velocity stack on the carb , I have had problems with them effecting carburetor operation and needed to find a different style of stack. Tune for the task, WOT in your case, you don't need to worry about response coming out of the turn.😀
That thing sounds like my wife after a spicy meal.
Very interesting stuff. Bike sounds cool even not running its best. Hope to run into you at BMST. I'll be the one in black race leathers.
You look like a skinny Jay Leno with the grey hair and the Canadian tuxedo. Well done Sir!
I think that's a compliment, so thank you!
We're riding out there in a few weeks! Looking forward to seeing your runs!
Going to be high and dry out at the flats
Definitely seems mid range / needle related. Since it's running lean at mid throttle with the needle in the top position, a thinner needle may be what it needs.
Jetting is a bit of a black art.
Yes, you are right about jetting being a bit of a black art. Thanks for watching...
If you need more midrange fuel and you are topped out on the clip you can add washers under the clip to go even higher.
Needle taper is the way to go here I think! You can grind them to get more mid-range fuel, less top end, stuff like that.
If that's Mikuni carb the number stamped on the jet is not a drill size for the hole through it, Mikuni do a chart to interpret the drill size of your jet from the number stamped on it, bear in mind that with Mikuni carbs the drill size is always a lot smaller than the jet number. Your issue with lean running is more likely down to the needle and atomiser combination, by all means shave down your existing needle which will richen it up but, do it progressively and test each time you file/shave the needle to check out the effect. Roland, HT Racing Ltd
Epic video through headphones 😵
Thanks Paul 👍
Thank you...
Go for it 👍
Thank you Mate!!
These are the Daves he knows, he knows. These are the Daves he knows.
Legendary reference for Canadians. If you know, you know....
I do know quite a few Daves...
Hi Paul, roughly speaking from quarter to three quarter throttle is all needle jet and not main jet. I also agree with Paul the dyno guy, unless the formula demands the original Amal carby put a Keihin on it or even a mikuni if you can’t stretch to the Keihin.
best episode in a while! keep it up.
You may look at the ignition pattern also. Maybe you are not getting the advance quite correct in the mid range which is hurting the high end pull. Good luck at the slat flats. Keep it straight on the black line. That's right they don't use the black line now.
It was the pipe and jetting. All fixed now.. Next video I will explain!
On the edge of my seat waiting to hear about Bonneville
We run adjustable main jets on our race sleds due to weather extremes. Do you think it could work in your case?
Stick at it Paul, if anyone can sort it, you can.
Ah the adventure that is jetting a custom motorcycle. One step forwards and two steps backwards.
Paul, I am sure you will be getting lots of suggestions on the direction of your jetting, but in all the conversations from main jet to needle and needle jet and pipe configuration nobody mentioned the slide cutaway. You have a lean condition in the mid-range, so some careful filing of the slide could help you.
I am stunned that as a man who never throws anything away, that you don't have your original jetting specs from your old 350.
Good luck, I am sure you will work it out.
when you file the cutaway larger, the mixture will become even leaner.. don´t know if thats the way to go..
@@vintagebike_ger ...my apologies. I actually woke up during the night and wondered what the hell had I said in my response to Pauls video. Thanks for correcting my error... 🙂
Hopefully with a little more tinkering you will get the settings sorted out 😎👍👍
I did get it figured out... Next video I will explain!
As you said better to sort out on the Dino than the salt flats Sounds like possible ignition timing as well
Cheers Chris
Friend of mine spent several years running dyno in Belgium, (former US Marine, met guy while training after service )
He told me they spent a lot of time setting airflow in the 'dyno room' to get closer to 'real world conditions' as if bikes were on the street at 100mph (or maybe 100KPH? I forget)
Guess I should get in touch with him as he's on Facebook.
Even though I watched the 'new' video first, it sounds like mid range is the issue which can be adjusted by needle taper. (only tried making a carb needle once, way too difficult but modifying is quite easy) I should probably watch video before commenting instead of stopping when I think of something
Short pipes will get best top end power but over a narrow rpm range and are a bear to tune for at lower rpm, (it's been 'quite well known' since Manx Norton in 1950's with 'megaphonitis')
Usual sidetrack, a Harley Sportster 883 with 'drag pipes' actually loses at least 4bhp as pipes are tuned length for a ~ 8,500 - 9,000 rpm motor.
Even after extensive dyno tuning they only get back to stock power output ( before setting up make about 40~44 bhp,
well, in early 2000's)
Is that Mustang Dynamometer from Australia?
k I have read good things about them.
That sure does sound like an intermittent ignition problem.
It might sound like that, but it's not. We went back to the Dyno, and now the bike runs fine. Tell you all about it in the next video...
It's nice work, regardless. Finding an optimal mixture throughout the throttle range looks deceivingly simple but is actually quite challenging.
Disappointing but that is what is so good with a Dyno session. I guess it one step forward and two steps back, but I know you'll sort it out. I also have to say that the bike looks great.
THE slide cutaway should be less. What is the cut away now?
From the sound of it, I think you have a very rich idle, is the fuel level okay? excellent work 👍😀
If that Tech said it would run better without the piston, I’d listen to him.
That’s Amal Mk2 have one in my BSA Gold Star.
2 things to check. You may need a deeper float and also the position of the pilot jet - 2 positions try both.
I'm not here to see the numbers I just want to hear that awesome engine..... This is gonna be good. 😁👏🖤
Messing with that mixture likely has the spark plug blacker than the Devil's heart!
I had a lean midrange on a Husky 430 CR that could only be corrected with a different slide. No amount of main jet or needle adjustment would correct it. Mikuni carb. Good luck.
Do you maybe have an air leak? Like a throttle shaft that is worn, letting unmetered air in? That would show up as a lean mixture at idle, correcting at higher RPMs.
A fresh needle may be in order as well, they'll wear against the inner bore of the jet, screwing up the taper.
Main jet only affects the top end. You could plug it and it would still run. You probably need to get a richer needle. You could have tried shimming the needle, that might have worked.
Some of those "Runs" sounded ignition related to me, but I'm not an Aermacchi guy, I own all Ancient Ducati singles - You might try and whole different carb, ie- more modern, I've seen a lot of fellas with good results from the new flatslides than trying to mess around with old-worn finicky Dellorto or Amal junk? I dont envy your situation
It does indeed sound like something is breaking down in the ignition system.
I can't help but be remembered the one night we had a ignition condenser in the distributor go bad in our race car. It started to run very rough in the mid-range and just wouldn't get out of the bogging mid rpm's. This continued for maybe 20-30 minutes of trying to trouble shoot until we eventually just lost all spark. Changed the condenser for one we snatched from the old water truck, and everything was fixed! I guessed the condenser developed a crack or a point that limited its capacity and over the short time just failed. But then i have seen motors that had the distributor shaft with the mechanical/vacuum advance freeze in place and do something similar with having poor midrange fuel ignition.
I am nt sure what you want from the bike. If its for flat out speed runs then its important to get wide open throttle power. If it is to be used on the road then idle and low end (part throttle) performance is the most important. I normally mess with cars and I have often seen people try to put carbs that are too large on their engines. This leads to slow airflow through the carb and makes it have poor response for the engine. High HC readings at idle usually mean that the engine is missing.
Time to try a larger carburetor. Not enough air flow.
Why would you be drilling out the main jet when it’s the midrange that’s rich? Should you not be looking at the needle jet and the jet needle in that range? Take the main jet out completely and run the bike. It should flood when opened fully but it should still be lean in the midrange.
I only had a couple of needle jets, and two needles... However, I did get it figured out, and I'll talk all about that next video. It was a big learning curve for me...
Hi Paul , just a thought ,you haven't got a two stroke needle in it ? , good luck,Nigel.
sounded like a bad case of megaphonitis which was a problem with race singles in the fifties with that sort of exhaust
I would think if you were thinking it was running on the choke it would be coming out the bottom of the bowl its jetted wrong to maybe the airbox or whatever stock air box or you remove the air box?
As others have said, attention to the main jet size was a mistake, as that is only critical at full bore. It may be worth experimenting with different size slide cutaways? I believe that the ones made for the AMAL mk1 fit as well, or is your mk2 a smooth bore? Frustrating when everything else is sorted.
spark
I guess this is where everyone puts in their two cents. Seems like the carb is so far off, I'd see if I could get it working with a K&N air filter installed and then after that see what it does with only the velocity stack. Otherwise you may just end up tuning for top end and sacrificing drive-ability.
Will the difference in height above Sea level make any difference with your jetting ?
Could it be an air leak somewhere in the carb or inlet?
Paul, Did you make it to Speed Week at Bonneville?
The idle "4 stroking" is likely too rich at idle, falling on its face when opening the throttle is a too lean midrange and is usually needle related, the clip should be lowered thereby raising the needle out of the jet some. The main jet is is usually only applicable at wide open. On an Amal the slide cutaway and needle are responsible for midrange (some would argue for emulsion tube involvement also). Dellortos are a different beast but may be similar. You could scan "Bushman's carb tuning secrets" for better information than I've got.
Thanks Lance. I did get it figured out, by making a Lot of changes. I will explain all next video...
Paul, put a VM34 Mikuni and a VAPE ignition on it and be done with it.
Mmmm, sounds like the main is too large but the needle taper and the cutout are incorrect. Carb being too large tends to make jetting difficult. Needs to develop air velocity to draw fuel and the stumble as at partial throttle.
Idle is idle, cutout has a big part til above 1/3 throttle, needle controls the wet side until it's all the way out of the metering housing only then are you fully on the main jet.
Another area to double check is float level and that the float valve and supply can deliver. Too rich at full throttle says there's enough for now. Covering the carb with a hand is needle and carb size. Start with needle but consider sourcing something slightly smaller as a backup. IMO
Interesting. but wow, that thing sounded terrible. Could it be something goofy like the cam is off 20 degrees? or some serious voodoo wrong with the ignition module? Best of luck figuring it out.
If the bike is rich wide open, then it is the main jet that is too big. If it's weak at 1/4 to 3/4 throttle then it is the needle & needle jet that is too small. There are not too many options with needle jets & needles on an Amal. Something else is wrong there.
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Get richer needle jets and jet needles.
I was embarrassed for all involved, watching this. It seemed like nobody had a clue about what they were doing.
That's right. Not a clue.
I think you need a new dyno guy if im being honest.
Cannot watch the video, and you are experienced. Another TH-camr was racing in Utah and it got wet, but he was too lazy to clean his vehicle. A lot of parts were unusable when he had time to clean. Interesting how quick that happens.
As soon as we get home, the whole bike comes apart...
It really sounded like the carb had an internal leak somewhere.. maybe even float level. Especially since the jetting wasn't really doing a whole lot. She sounded like an absolute weapon though! good work.
man that sucks you didnt get a clean pull, the bike looks great though. im not as learned as you on these bikes but im definitely suspicious of either that carb or the ignition.
I would think if you were thinking it was running on the choke it would be coming out the bottom of the bowl its jetted wrong to maybe the airbox or whatever stock air box or you remove the air box?