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Thu Nov 19, 2009 7:37 am

Since I'm having troubles adjusting the carburetor, even after a rebuild (it's a Bocar unit), I started looking for vacuum leaks. I sprayed carburetor cleaner from beneath and got at least a few hundred rpm rev on the cyl. 1/2 side. I'm puzzled, because it rev'd up both when I sprayed between the head and the cylinders, and also when I sprayed between the cylinders and the case.

Basically, I'm shooting the cleaner near both ends of the push rod tubes.

However, I have good compression on that head, 130psi on cyl. 1 and 2.

Could it still be the head gasket? Or is the cleaner wafting up somewhere else?

Thu Nov 19, 2009 7:41 am

Huh?

If you have a vacuum leak it's between the carb and the head, so spray the base of the carb, the boots on the manifold if it's a dual port and where the manifold mates with the heads.

Spraying underneath has nothing to do with a vacuum leak.

Thu Nov 19, 2009 8:31 am

technically on the intake stroke it is possible to have a vacuum leak where the head meets the cylinder, but you would have to have way loose heads. However, if you do have loose heads, it is called a compression leak.

Thu Nov 19, 2009 9:44 am

Then, that still doesn't explain why the engine revs up immediately when I spray the carb. cleaner from underneath on the passengers side. From what you're saying, it shouldn't rev up when spraying down there. It is not reaching the carburetor base or the boots. It doesn't rev up when I spray where the intake manifold is bolted to the heads from above either. Pretty strange! Help!

Thu Nov 19, 2009 10:56 am

Quote:
PostPosted: Today 9:44 am Post subject:
Then, that still doesn't explain why the engine revs up immediately when I spray the carb.
Ahh.. you are missing one critical fact. On the passenger side is where the warm air intake is for your aircleaner. when you spray carb cleaner down at the heads, the fan pushes it to the rear, and get's picked up by the warm are pickup tube. Thant's why revs go up.

Thu Nov 19, 2009 11:56 am

I think you hit it on the head. Now I'm blushing for being so stupid. That must be it. Thanks,