too rich

on start up till my bike gets warmed up it puts out black smoke when u give it throttle, it goes away though, what is this an indication of, to rich jetting or something else, the valves were a little on the tight side when i checked last night, thanks


It sounds like the pilot circuit is too rich. Try adjusting the fuel screw in 1/2 turn and see if it goes away. If the fuel screw is or ends up tighter than say 3/4 turn, you will probably have to go smaller on the pilot one size.

I'm not sure what the problem is, but this sounds likely. It is cheap to find out.

Good luck,


hey matt i have a 2002 426. closed to 1/4 trhottle it puts out apuff of black smokeand stumbles alittle even when warm . ihave gone up and down on piot 40 42 45 it slill does the same if yours does this let me know . ive taken to dealer they cant fix it . my next step is new accelerator pump diaphram. thanks larry in colorado

freestyler and others, you still have to do the BK mod. The accelerator pump just puts out way too much fuel.


We all agree they used to. I am not sure they still do. The '01 250Fs varied but most didn't. DOC is finding 426s with too little squirt. I'm not sure I'd do the BK mod unless it had long squirt symptoms.

Freestyler said somewhere else that it happened with he rolled it on, in gear or in neutral. If rolling it on and not blipping it, the AP would be muted. I'm not sure AP is his problem.

Good luck,


Im not sure if this is your problem... but when high compression engines are first started, the rings dont have a great seal against the cylinder wall. Thus allowing a tiny bit of oil to get past and into the combustion chamber.

As the engine heats up, the piston and rings actually expand and make a much better seal, thus no oil or black exhaust.

If it smokes a little at first and then clears up, that is normal. I had a 410cc engine in a quad with 13:1 compression and it did the same thing you mentioned. However, if there is an excessive amount of black smoke, then you're probably too rick somewhere in the jetting. :)

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