I've got an '82 Yamaha XJ 750 Maxim. I rebuilt the carburetors this weekend, and after putting it back together, it seems like it's got a vacuum leak. There's a loud squeal every time a cylinder fires.

I noticed it was coming from one carb body in particular, so I sealed the rubber gasket... thing that connects the carb to the engine block with some Permatex silicone gasket. That reduced the noise at idle a lot, and the noise is completely gone when revving/accelerating.

After getting the engine speed up, it takes quite a while to settle down again. Sometimes, it actually races itself up higher and higher instead of settling. Needless to say, I'm not riding it right now.

Any diagnosis, and what I can do to fix it? Thanks in advance.

1 Answer 1


I figured this would be the problem.

Turned out someone before me forced an SAE 1/4" bolt into the M10 hole on the engine block, and that's exactly where the vacuum leak was. I had a mechanic put a helicoil in, and the problem has gone away.

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