Leak,...intake or exhaust?

[UncleMike]

I hear a definite hissing sound from my engine, but it sounds like it comes from the top of the engine or the front. I have very supple boots on the carbs and the clamps are tight. I do however have one broken exhaust bolt.

The fact that the bike will idle around 2100rpm's after about thirty seconds to a minute after startup, or directly after revving leads me to believe it's an intake leak, but I can't imagine where. If I've got a good seal on the boots, is it possible that the manifold o-rings could still cause a leak, or is it more likely the broken exhaust bolt?

[gspaul]

The water mist method seem's to show up intake leak's pretty well, the motor will misfire if there is a leak.
It does sound like an intake leak, the exaust wont hiss.
But normaly it's hard to hear a slight vacumn leak, unlike a car that has vacumn hoses all over the place and if one comes off you can often trace it by ear.
Had to do this last week on my wife's Ford,it all of a sudden would only idle at 2 grand.
2 hour's of pulling everything off and checking every hose, got it in the end.
Maybe also check the vacumn hose to the petcock , and the petcock it self for air leak's.

[duaneage]

Spray a little wd 40 or carb cleaner around there with a plastic tube and see if the engine speeds up or not. Then you will find the intake leak

[UncleMike]

Cool. Thanks guys.

I would assume that WD-40 would be less harmful than carb cleaner?

[duaneage]

carb cleaner will not hurt anything , wd 40 might make the bike squeek less :P

[gspaul]

Not certain why anyone would want to use carb cleaner!

[duaneage]

Not certain why anyone would want to use carb cleaner!

The carb cleaner that comes in a spray can will speed up the engine if drawn into a vacuum leak. It also will clean off the parts so cracks can be seen. It also cleans the throttle and choke linkage off so leaks can be found there as well. That is why it is called carb cleaner. :P

[gspaul]

A water mist has a much clearer result, the carb boot that you spray totaly stop that cylinder fireing if it has a leak, I tried WD on my intakes with little result.
Perhap's because my leak's where minor, the water worked better for me.
But good idea for cleaning the throttle and choke linkage.

[UncleMike]

Plus, wouldn't the cleaner dry out the rubber?

[earlfor]

I just use an old windex bottle with water in it. Works fine for me.

Earl

[UncleMike]

And I'll notice the bike backfiring when I spray if there's a leak?