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Discussion Starter #1
Hi there
I have a VN750 with what seems a fuel / air / ignition problem. It refuses to rev properly over 5k RPM smoothly - when I can rarely get it above that it sounds great! Appears to idle ok. This is when running on the centre stand, havent even ridden the bike that 2 feet so far! Grrr - thanks E-bay, simple fix my a$$.! :mad:

Local garage advised me to get a used pair of carbs and try them (great advice?)- well, got some and exactly the same problem.
I think it is a Japanese import (1985) - VIN number VN750A000535, I am in the UK.

I have since replaced all the plugs and plug caps - the existing plugs were sooty black indicating too rich a fuel picture. What I have noticed that on the right hand carb (as you sit on the bike) - the old set of carbs had a rubber stopper over an inlet/outlet at the rear of the r/h carb. This one is open and I do not have a clue whether I should block this, leave it open. It does create a vacuum when running - I guess its some emission thing not required in the UK. It does make a diference when blocked or open but does not sure the running problem.

Next steps gratefully received, otherwise it's £45 / hour in the local dealer...:(
 

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Premium Member
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3,505 Posts
Hi there
I have a VN750 with what seems a fuel / air / ignition problem. It refuses to rev properly over 5k RPM smoothly - when I can rarely get it above that it sounds great! Appears to idle ok.

What I have noticed that on the right hand carb (as you sit on the bike) - the old set of carbs had a rubber stopper over an inlet/outlet at the rear of the r/h carb. This one is open and I do not have a clue whether I should block this, leave it open. It does create a vacuum when running - I guess its some emission thing not required in the UK. It does make a diference when blocked or open but does not sure the running problem.
There should be a boot running from the bellmouth of that carb to the airbox - when riding, this allows relatively "still" air (and filtered!) to enter the carburetor so that the vacuum set-up works right. Lance328 might pop in on this one, but it's possible that without the boot, you're taking too much air into the carb and it's probably running lean on the OEM main jet. Do you have a boot for it?
 

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Discussion Starter #4
Hi there
Thanks, Ok - plugged it off, it is at the rear of the right hand carb. Still running rubbish though. Any ideas guys?
Cheers
Tony
 

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Discussion Starter #5
Think I've sorted it!!!

Checked the air filter connectors and they were not on quite right plus the vacuum hose from the pet-cock to the left hand carb had a virtually invisible slight split in it.
Got a mate coming around on Friday to balance the carbs properly for me and that's it. First road trip next Saturday / Sunday!!

CHUFFED!

Tony
 

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D2u
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Sounds like your on the right path.Hope you and you M8 get it running good.:smiley_th
 

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Discussion Starter #8
I certainly hope so!!

I've had the bike for nearly 2 months and have gone nowhere. We finally have some stunning weather over here and it would be WRONG WRONG WRONG:) to not take advantage!
 
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