Premature revving problem - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 7 (permalink) Old 04-10-2018, 03:54 PM Thread Starter
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Premature revving problem

I'm working on a 2001 Yamaha V Star 1100 Classic. Last year I installed a Hypercharger and full Cobra exhaust system. I've tuned the carbs to closely match my intake and exhaust configuration, however, I'm having a persistent issue with the bike. I don't remember if the problem existed prior to the mods. With the bike running, in neutral, and I give it just a little bit of throttle it revs up quite a bit. It's not a gradual increase. Today I thought it might be a good idea to check and make sure the carbs were in sync, which they are. But, I noticed that when it revs up, the front cylinder starts pulling way more vacuum than the rear cylinder. If I hold the throttle steady, eventually the vacuum will even out between the front and rear.
I also found no vacuum leaks. Diaphragms are seated and are in good condition.
Help please & thank you!!
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post #2 of 7 (permalink) Old 04-10-2018, 07:25 PM
KCW
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did you just pull the bike out from its long winters rest for the first time?

If you didn't have a fuel stabilizer in the gas over the winter, it sounds a lot like something we have been talking about in this thread:

https://www.starbikeforums.com/forums...lem-650-a.html

most likely running lean because the jets have goop in them.

reading your post again, did it ever run right after you made the mods?

I might be jumping to conclusions.

Did you set the PMScrews by turning them out a prescribed number of turns, or did you follow up by then adjusting / dialing them in?

If you search on adjusting PMS there are a couple threads on how to adjust them after you initially set them to the number of turns from the mods table.

Last edited by KCW; 04-10-2018 at 07:29 PM.
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post #3 of 7 (permalink) Old 04-10-2018, 07:51 PM
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Thoughts to ponder. Vacuum is created by cylinder sealing. Piston rings seals to wall with valves opening and closing with engine spinning creates vacuum. No two cylinders will make the same vacuum but should be close. I would perform a cylinder pressure test. This would eliminate any engine issue. I've chased simular issues in the past with dissimilar vacuum and every time provided the internal engine was good the issue was the carbs. If cylinder pressure is good on both cylinders it's a carb issue. Just my thoughts from experience.
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Les B.
2001 Vstar 1100 Classic (sold), Cobra Slash Cut full exhaust, Dropped 1 inch with lowering links, ORK, 4.5 inch handlebar risers, Ultimate passenger seat, Passenger pegs moved forward 4 inches, Handlebar clock, KN air filter, Viking saddlebags, Additional rear lighting
Loose nut "me" behind the bars
2006 Harley Electra Glide Ultra Classic

https://sites.google.com/site/vstar1100kb/home
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post #4 of 7 (permalink) Old 04-10-2018, 08:16 PM Thread Starter
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Quote:
Originally Posted by KCW View Post
did you just pull the bike out from its long winters rest for the first time?

If you didn't have a fuel stabilizer in the gas over the winter, it sounds a lot like something we have been talking about in this thread:

https://www.starbikeforums.com/forums...lem-650-a.html

most likely running lean because the jets have goop in them.

reading your post again, did it ever run right after you made the mods?

I might be jumping to conclusions.

Did you set the PMScrews by turning them out a prescribed number of turns, or did you follow up by then adjusting / dialing them in?

If you search on adjusting PMS there are a couple threads on how to adjust them after you initially set them to the number of turns from the mods table.
I did use stabilizer over the winter. Jets are clear, I had the carbs out for inspection today. I did not turn the screws out a prescribed number of turns, I turned them out by experience I guess I would say. Currently at 3 1/2 turns out from bottom.
I just can't imagine this bike is running lean. Front cylinder has a 125 main, 20 pilot, needle adjusted to the bottom groove. Rear cylinder has a 130 main, 20 pilot, needle adjusted to bottom groove. The bike runs great through the entire throttle range, it's just the revving issue.
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post #5 of 7 (permalink) Old 04-10-2018, 08:19 PM Thread Starter
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Quote:
Originally Posted by lesblank View Post
Thoughts to ponder. Vacuum is created by cylinder sealing. Piston rings seals to wall with valves opening and closing with engine spinning creates vacuum. No two cylinders will make the same vacuum but should be close. I would perform a cylinder pressure test. This would eliminate any engine issue. I've chased simular issues in the past with dissimilar vacuum and every time provided the internal engine was good the issue was the carbs. If cylinder pressure is good on both cylinders it's a carb issue. Just my thoughts from experience.
I have the tools and ability to perform a compression test. I think I will try this tomorrow night after work just to eliminate it as a possibility. Thank you for your thoughts.
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post #6 of 7 (permalink) Old 04-10-2018, 08:42 PM
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Here's a link for some info on hyperchargers.
https://sites.google.com/site/vstar1...-modifications
I have a few friends who put hyperchargers on and could get them to perform either full throttle or lower RPMs, never both. They always had them set up full throttle. Here a few snap shoots of info in link. Good luck and keep us informed.




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Les B.
2001 Vstar 1100 Classic (sold), Cobra Slash Cut full exhaust, Dropped 1 inch with lowering links, ORK, 4.5 inch handlebar risers, Ultimate passenger seat, Passenger pegs moved forward 4 inches, Handlebar clock, KN air filter, Viking saddlebags, Additional rear lighting
Loose nut "me" behind the bars
2006 Harley Electra Glide Ultra Classic

https://sites.google.com/site/vstar1100kb/home
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post #7 of 7 (permalink) Old 04-11-2018, 08:54 PM Thread Starter
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I just finished a compression test. Both cylinders are at 130 lbs.
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