New exhausts poor running

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When you are tuning your carbs, first make sure your ignition timing is correct for the fuel octane ration and do not change it. You jet to suit the timing and comp. ratio.. Fit main jets which you know to be too rich. Then start the bike. If it runs cleanly and does not cough or spit back through the carbs, your jetting is in the ball park. Take the slides out and put the needles on the clips in the top grooves. If the motor does not cough when you ride the bike, your needle jets are too large. With the right size needle jets, you should be able to progressively lower them until you induce the cough. When you get it- raise the needles one notch. You should only use plug colour when setting the main jets. If you look at the porcelain, right down inside the plug. There should be a about 2mm black ring there after you have ridden the bike flat out for at least a mile. If you use a hotter plug for tuning, you should stay safe. The heat range of the plug determines how fast the soot burns off the porcelain.
If you want more performance, use slower taper needles, but your tuning might become more weather-dependent. When you tune a motorcycle, cause and effect are by interaction of several variables - not just two.. You need to recognise the pattern, if you want to optimise performance.
The exhaust system can easily take a thousand revs of the top of the usable rev-range, if you only change one thing.
 
My 2 cents...and this may or may not be your problem. It's a potential variable that I like to permanently take out of the equation.
The heat insulating phenolic spacer is not the best gasket. And checking it with the spray can method is not accurate. For proof try using yamabond on both sides of the phenolic, bolt it up and run it for a few miles or more. Then remove the manifolds and you'll see every trace of the yamabond is gone....sucked into the motor.
My solution is to make a sandwich of paper gasket - phenolic - paper gasket glued together with yamabond. Then use yamabond between the motor and the sandwich then between the sandwich and the manifold. This combination is AIRTIGHT.
** make sure the sandwich is not obstructing any part of the airway. I use an exacto to trim out anything in the way.
** consider this semi-permanent. If you want to remove the carbs in the future, use allens on the carb flange...leave manifolds in place. The carb o-ring does a good job by itself...no need for a gasket or sealer here.
** and, of course, make sure the carb flange is not warped.
 
acotrel said:
When you are tuning your carbs, first make sure your ignition timing is correct for the fuel octane ration and do not change it. You jet to suit the timing and comp. ratio.. Fit main jets which you know to be too rich. Then start the bike. If it runs cleanly and does not cough or spit back through the carbs, your jetting is in the ball park. Take the slides out and put the needles on the clips in the top grooves. If the motor does not cough when you ride the bike, your needle jets are too large. With the right size needle jets, you should be able to progressively lower them until you induce the cough. When you get it- raise the needles one notch. You should only use plug colour when setting the main jets. If you look at the porcelain, right down inside the plug. There should be a about 2mm black ring there after you have ridden the bike flat out for at least a mile. If you use a hotter plug for tuning, you should stay safe. The heat range of the plug determines how fast the soot burns off the porcelain.
If you want more performance, use slower taper needles, but your tuning might become more weather-dependent. When you tune a motorcycle, cause and effect are by interaction of several variables - not just two.. You need to recognise the pattern, if you want to optimise performance.
The exhaust system can easily take a thousand revs of the top of the usable rev-range, if you only change one thing.
Click to expand...
Thanks for the technical run through which will be useful if I decide to tune the bike still further. However, the bike ran perfectly when I first jetted up to 280s, running up to and beyond the redline very smartly, and also ran about as well with the 300s albeit maybe a little bit heavier. I think the issue of poor running at closed throttle is a leak that happened after the second jet fit, whether caused my me or just coincidental I am trying to find out and will be ticking off the likely suspects suggested so far one by one and let people know how I get on.
 
PM999S said:
With throttle closed...
Click to expand...
With the throttle closed and warmed up, closing the chokes should kill it - not make it run faster. You either have an air leak or the air screws out too far and the throttle stops adjusted to compensate or think the chokes are open when closed.
 
I'm happy to report that the good burghers of this forum have come up trumps again! Having replaced all the suspect parts suggested I found bolts on the right hand manifold were fairly loose and signs of weepage. New insulators fitted with a smear of silicon sealant and the bike runs pretty well now. Still a little grumpy on closed throttle but no detonating in the exhausts and pulls strongly and sweetly from low revs. I take the arguments about silencing on most engines but I believe the early production racing 2-into-1 system had no baffling and seemed to do well. All I know is the bike revs quicker and cleaner to the redline than with the old Long Range system fitted and that was hardly quiet! Thanks again all.
marshg246 said:
With the throttle closed and warmed up, closing the chokes should kill it - not make it run faster. You either have an air leak or the air screws out too far and the throttle stops adjusted to compensate or think the chokes are open when closed.
Click to expand...
 
I always think , if it wont run right , take the Mufflers OFF . start it up . Quick Blat . If anyone complains theyve got a weak set of priorities . Tho did live in the sticks .
Lotta places now their hair would stand on end and theyed have heart attacks , and pulminary something , appolexy & indigestion , if you drove a real car .

If it goes spastic when you refit the mufflers - theyre No Good . Use them for defence when the storm your driveway .
 
Matt Spencer said:
I always think , if it wont run right , take the Mufflers OFF . start it up . Quick Blat . If anyone complains theyve got a weak set of priorities . Tho did live in the sticks .
Lotta places now their hair would stand on end and theyed have heart attacks , and pulminary something , appolexy & indigestion , if you drove a real car .

If it goes spastic when you refit the mufflers - theyre No Good . Use them for defence when the storm your driveway .
Click to expand...
That 2nd paragraph sounds like a retirement village ! ? . :)
 
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Good that you found the issue.

If it's popping and banging on the overrun it's an indication of air leaks in the exhaust, and shouldn't be detrimental to performance? Race bikes with spring-retained systems are a good example.

I can't comment from personal experience, but I'm sure I've read that the K&N filter performs poorly against the original Ham-can type?

But those main jets.... As already said, they only affect WOT and the approach to it, where most of us road riders hardly ever live; except when checking if we've got the right main jets fitted :)

I've also been amazed at how much difference new throttle needles and needle jets can make. My most recent rebuild simply wouldn't rev past 3k (yes, the new needles & jets were still in the bag). It was that bad I'd assumed the new EI was faulty, but once the carbs were rebuilt with the new stuff fitted it ran perfectly, and on the original - assumed knackered - 1970 carbs.
 
B+Bogus said:
Good that you found the issue.

If it's popping and banging on the overrun it's an indication of air leaks in the exhaust, and shouldn't be detrimental to performance? Race bikes with spring-retained systems are a good example.

I can't comment from personal experience, but I'm sure I've read that the K&N filter performs poorly against the original Ham-can type?

But those main jets.... As already said, they only affect WOT and the approach to it, where most of us road riders hardly ever live; except when checking if we've got the right main jets fitted :)

I've also been amazed at how much difference new throttle needles and needle jets can make. My most recent rebuild simply wouldn't rev past 3k (yes, the new needles & jets were still in the bag). It was that bad I'd assumed the new EI was faulty, but once the carbs were rebuilt with the new stuff fitted it ran perfectly, and on the original - assumed knackered - 1970 carbs.
Click to expand...
Actually I did buy new needles which I haven't yet fitted but will certainly do so on reading your findings!
 
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