02 YZ426 questions

I changed the exhaust to a quieter one for SM riding (don't know what brand/make, got it with the bike), also the header pipe, and noticed that there is no gasket, or it's a lot thinner than the gasket on the original one between the header pipe and the rest of the exhaust (slip-on muffler on pipe). Can this cause excessive popping? It's not like popping 2-3 times louder on decel, it's popping continuously like machine-gun fire :) Or mixture problem? (Put Hot-Cams exhaust cam, but didn't adjust anything in carb). What can I use as a replacement gasket? Is it something Yami specific, or can I get it from automotive stores also?

the yamaha washer is a copper crush washer - likely, yours has had it - before playing with your jetting (which could also be a problem) I would go get a new washer first - at least you will know it's sealed for sure before hunting other areas..

It's worth checking the header/head gasket, but the gasket he's talking about is at the joint of the header to the mid pipe. Most after market exhausts do not have a gasket here, and some can leak a significant amount of air when they get old and loose. This could be the cause of your decel backfire, and should be checked before trying to correct it with jetting/adjustments.

If it does leak, try some high temp silicon sealer. Let it cure for 24 hours before running the engine.

Bear in mind that some decel popping is a sign of a well calibrated YZ426/450, so don't fight to eliminate the last little bit of it to the point that you have your idle richer than it should be.

Yes, grayracer, I'm talking about that gasket. Will try the high temp silicone, but would like it better to have some "real" gasket there, because I know that silicone is a kind of rubber, but it's not meant to support vibrations and can get loose of the surfaces, and then it will seal as a simple "O" ring.

Maybe the stuff that is inside the silencer, don't know what's the name...wool, or what the ?@%! is it's name :)

BTW how to check if it's leaking? Start up the engine and plug in the exhaust?

No doubt that I misread it with the best of intentions :)

That's one way, but it doesn't tell you whether it is drawing in air during operation.

The pipe was made to provide an adequate seal with no gasket at all. Running a film of silicone is a valid method of sealing older ones that loosen and leak. Us a high temp type, black seems to work best, for some reason, and let it cure as I said. If the leak is at that point, and causing your problem, this will immediately affect it.

As the engine runs, the silicone will actually "burn" to a harder remnant of itself, and will seal the exhaust quite well for some time.

The whole machine-gun popping was because of too lean idle :thumbsup:

Adjusted the carb yesterday (idle-mixture), took it for a ride, and now it only popps 1-2 times on hard decel, that's normal.

Yea the popping is due to beign too lean, i would just turn your fuel screw out a 1/4 of a turn.

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