Hey guys so i have two yz 426fs and they both have the same problem.....they will start right up with the choke out but literally the second its pushed in they die....all the jets in the carb are clear so im kind of stuck....ANY imput would ge great


And my float is set correctly as well i forgot to mention

It sounds like the idle circuit is lean or blocked. I know you said the jets were clear, but a pilot that looks clear can be 40% or more obstructed by a varnish deposit you can barely detect.


Also check the hot start plunger to make sure it closes, make sure there's on O-ring on the pilot screw, and check the vacuum release plate on the engine side of the slide. It's a common mistake to assemble them upside down (the square edge goes down, not the half round one), and they will crack or chip due to wear and cause all kinds of trouble.

Where does the o ring on the pilot screw go?

The order coming out should be... screw, spring, washer, o-ring. The o-ring might hang in the carb when taken apart then fall out as it relaxes. Two days of cussing before i figured mine out.

i had the same issue on my 01 426. i changed the pilot jet from the stock 42, to a 45. the bike has a fmf power bomb header & fmf power core muffler and no lid on the airbox. the main jet is 68 and the fuel screw is set a 2 1/4. jet's are about $4 a piece, i see no reason to even think about drilling out a jet

No one is suggesting drilling a jet.

i must have misunderstood that link then. i apologize

What I said was to use a drill as near to, but no larger than, the jet size to clear a varnish deposit, holding the drill itself in your fingers, preferably. In fact, I usually recommend pushing the shank of the drill through, rather than the cutting end.

Had almost the same issue on my 02 426, would start on choke fine then would barely run with the choke off, had to keep the idle high to prevent it from shutting off.

When trying to rev it or ride it, backfired real bad. Cleaned the carb and jets thoroughly, twice, no change.

Turned out to be a bad CDI unit, as soon as the RPM's increased the timing went all to hell.

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