Vacuum Leak - intake boots

Are there any tricks to getting a really tight seal on the engine intake manifold?

After putting my carbs back on I can't get the engine to respond to throttle, it just bogs out. It idles, but only for a minute or so until stalling. I have my engine boot clamps tightened down as far as they'll go and the carbs pushed all the way into the boots, flush with the rubber. When idleing, if I spray a little pressurized air or cleaner near the edge of the boot where the carb body rests, the engine responds. I inspected the rubber and it looks good as new, no cracks and its very pliable. The only thing I can think is that my clamps are warped and worn out so they don't make tight enough pressure around the whole boot. Anyone had this issue? I'm sure I may have other problems but that vacuum leak is almost undeniable so i might as well address that first, right?

1982 KZ550-C3 (LTD)

Buy some new boots.

Have you replaced boots and reused the same clamps before?

Unless they are damaged or not the correct clamps you should be able to reuse them. If for some reason you cannot, they are still an "Active" Kawasaki part so any online or local dealer can get them for you. Partzilla lists them at $4.35 each. Ed

find.partzilla.com/?r=t&q=92037-1129&x=12&y=10

The boots will seal around the carbs spout without any clamping force. The clamp is there to make sure the carb do not back out, it does not make the seal. The seal is achieved by the grooved intake manifold and the corresponding bump on the carb spout. So do not overly tighten that clamp should just be snug.
If you are getting leaks it's probably going to be at the sealing surface between the head and manifold face. I have used many an old manifold with success by appling Yamabond #4 or equivelant to the mating surface of the intake manifold, installing it and letting it sit overnight. Seals it right up. DO NOT use silicone it will just rot away from the gas.

A vacuum leak should really only affect idle. The amount of air leaking becomes negligible when the throttle is opened, so you may have some other issue.

Are you sure you are running on all four cylinders? If the engine sounds really rough and reluctant to getting throttle, it may only be firing on one pair of cylinders. Do a water spray test on the exhaust to compare the cylinders and see if one or more are not firing.

Like Baldy says, it takes almost no clampling force to get a good seal from carb to manifold, as long as everything is seated properly, and in the right position. On the 550's, the manifold has the semi-o-ring cast into the rubber, and the carb has a groove for it. I suaully leave the manifolds loose, then install the carbs, then snug up the manifold bolts so that the carbs set the spacing on the manifolds. But it's trick to do that since it's hard to get to the mounting screws when the carbs are in place. (I convert the cros-head screws to short hex bolts.)

I suspected there would be a leak right against the head but troubleshooting that with a spray can proved it was on the carb side, not against the head (but I still bought some of that fuel resistant gasket maker stuff to slather on when I finally install them again).

I have noticed that o-ring in the carb holders and the corresponding groove on the carb spouts. I guess I never checked the condition of the actual o-ring, but I suspect the entire rubber pieces are all little warped and so I'll need to get new boots.

Good point about the vacuum leak only affecting idle, but can't see any other issues. I've monitored the heat of all 4 exhaust pipes and also the exhaust pattern on both mufflers... seems pretty consistent accross all 4. Soaked all 4 carbs (without o-rings!) in chem-dip, hard to imagine something is clogged. Honestly don't want to think about anything but the vacuum leak for now or I might lose hope.

Yep, carb boots are like tires. You don't want old, hard rubber.


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