Intake Boots, Vacuum Leaks and Gasket Goop

Vacuum leaks turn up here as one of the usual susupects for a number of carburetor related problems. One of the obvious places for that to happen is on the downstream side of the rubber intake boots where they are bolted to the cylinder head.

I had a mechanic tell me to "always" use a liquid gasket material at that point. In fact, he specified Yamabond 4 as the material of choice.

Now, the Kawasaki service manual does not specify any such bonding agent (at least not for my KZ440).

So, the questions are: Do you folks use a bonding agent when attaching intake boots to the block? If so what? It seems like something that can't hurt, but since the manual doesn't ask for this, is there some potential downside to doing it?

Mostly just curious here, but I will be bolting these things back on my bike soon and would be happy to avoid problems ahead of time.

mwriders wrote: Vacuum leaks...One of the obvious places for that to happen is on the downstream side of the rubber intake boots where they are bolted to the cylinder head.
I had a mechanic tell me to "always" use a liquid gasket material at that point. In fact, he specified Yamabond 4 as the material of choice....

Imo, application of any sealant between carb holder and cylinder head, Yamabond or otherwise, is ill-advised.
The Yamabond folks don't claim it's gasoline-proof.

Am unaware of an assembly sealant that's both heat-proof and gasoline-proof which could be relied on for long term service and durability in this particular application.

Would heed the FSM.

Good Fortune!

Thanks, Patton. I asked because the mechanic's specification of Yamabond was a red flag. I know for a fact that the stuff isn't gasoline proof. Learned it the hard way.

mwriders wrote: Thanks, Patton. I asked because the mechanic's specification of Yamabond was a red flag. I know for a fact that the stuff isn't gasoline proof. Learned it the hard way.

I had to use it on my intake manifolds last time (about five years ago) so they would seal. I put a tiny bead around the surface of the manifold and then use a razor blade to scrape it so it leaves the thinnest possible layer. Let dry overnight then attach. It acts like a super thin gasket.

I used the Ultra Black Hi Temp sealer but 3-bond is at least as good as that. The bottom line is it's not fuel proof, but you should not have standing gas there anyway and it's a very thin seal layer. Mine has held tight for five years of use. If you don't use it and have leaks, you will have nothing but problems.

When I replaced my carb holders 7 years ago I put them on dry - no sealant. They still do not leak at all, so I would recommend dry. Ed

It should be possible to put them on dry but last year I gave up and used Permatex #1 which is supposedly fuel resistant and good for these temperatures - I was getting some spit back at low speeds through the carbs. One year later and all I can say is so far so good

I've used Three Bond on these manifolds with good success with no signs of it lifting or separating. Don't use silicone. The Permatex might be good here too.
I wouldn't use this on new manifolds. The reason for use is on old manifolds cracked at the mating surface.
As far as long term (over a couple years), I can't tell you. Short term, seems good.

Been using Yamabond #4 for that exact application for many years now with no failures. I have used some pretty mangled intake manifolds using the stuff with great results.