my 2002 400ex just wont start but wants to

[01 RAPPY 660]

The main jet should me screwed in until it is snug, so it sounds like you have it right. I would first try adjusting the pilot screw, it should be on the underside of the carb, in front of the float bowl. Start by turning it all the way in and then back it out 2 turns. See how it works and try adjusting it back and forth to see if there is any improvement. You will also want to make sure the float bowl vent line is not clogged. The tube for it comes right out of the bottom of the float bowl, make sure you can blow air through this line.

the fuel bowl line is clear/clean its not clogged. and thanks ill try adjusting the pilot screw and see what happens.

if that pilot screw dont help do you know where to look next?

thanks

[01 RAPPY 660]

well i had the throttle cable on the thumb throttle turned most of the way in so i backed it out and got it to idle by its self now but its still has a rough idle. and when you rev it slowly it wont rev smooth it hesitates as in its cutting out or being choked out a little. about mid throttle on up its just fine though. im thinking maybe when i drilled out the pilot jet to clean it, i made the jet hole size bigger but i dont know for sure. and i adjusted the pilot jet screw and it made a little diff but did not quite fix the problem. ohyea im now running aether a .30 or .40 over sized piston would this make a diff??

Edited March 25, 2010 by yamahabansheeboy

[DirtDemon]

The piston size should not make enough of a difference to matter. From the sound of it, you are on the right track with the pilot jet. It sounds like all your problems are happening in the range that would be affected by the pilot, so I would replace the jet with a new one and see if that works.