New 02 YZ426

My new YZ426 came off the floor needing a new sparkplug. That put an end to most of the backfiring. However, it still seems to pop and crack when decelerating. Is this normal? I rode someone's '01 426 and it didn't do that. Any suggestions appreciated.

Merry X-mas,

More than likely your lean in the pilot circuit. Turn the fuel screw out (located on the bottom of the fuel bowl) 1/4 turn at a time. But first, turn the screw in and count the number of turns it is. That way, you can always return it if you get to far off.

If you get to 2.75 turns out, that's a good indicator, that you'll need to go up one, on the pilot jet.


I have put about 30 hours on my 2002 yz426, and I have yet to notice any backfire problems.

426Brent didn't say where he lived or the temperature. A hanging idle, slight popping/backfiring on decel is indicative of a lean pilot circuit. Colder weather requires richer jetting. I live in Houston Texas where the stock jetting and 1.5 turns on the fuel screw (on my stock bike) is pretty good when the weather is 70-80 degrees. Right now is it barely 40-50 degrees and I have had to use 2.75 turns on the stock 42 pilot jet to get it started and running. It needs a 45 now but I haven't received it from mail order yet!

So, with a stock 2001 / 2002 bike turning the fuel screw in and out will compensate (at sea level) for a pretty wide range of temperatures - colder than 40-50 should probably have a 45 pilot.


Steve T

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