[jayhawk]

imported post

I am baffled, sometimes the bike runs like you would expect and another time it starts running lean, causing knocks,and backfires. Running on choke fixes the problem. Why not all the time if the jets are plugged? Also I’ve notice the gas tank is either building pressure or a vacuum as you can hear a noise coming from it after it is shut down. Opening the cap I believe relieves the pressure but it might be the reverse instead. Any ideas? I would like to know for sure that it’s the carbs before I crack them open. Just what does the air cut off valve do and could it cause the kind of problem I’m experiencing?

 

[ALEX BERECZKY]

imported post

jayhawk wrote:

I am baffled, sometimes the bike runs like you would expect and another time it starts running lean, causing knocks,and backfires. Running on choke fixes the problem. Why not all the time if the jets are plugged? ...

> I had a sport bike that did that, due to an air leak... the Rubber Boots, connecting carbs to intake manifold were worn out...the extra air leaking in would lean out the air/fuel mixture.

The fix for that would be to put Air Filter Grease around the inside of the boots during carb installation and also replace the boots if req'd.

You could detect such an air leak by spraying engine starter around the carb/manifold joints while the engine is running... if the engine speed increases, then you've got a leak.