Problem 400ex

[WOracing]

Ok ive had enough with messing with my 400ex. i bought it new in 03 and it was good up until 4 months ago. We piped it and rejeted and it ran fine for like a month and a half and then all of the sudden it wont idle or run right, it sputters and backfires all the time. I already flushed the carb once and it was good for about 2 weeks...any ideas anyone???

[WOracing]

So does that mean no one knows whats wrong?

[JDiablo]

put this in the powertrain forum..you will get more replies,and most likely your jetting is off

[Chef]

Did you try maybe putting a spark plug in it?

[WOracing]

Originally posted by Chef
Did you try maybe putting a spark plug in it?

yes that wasnt the problem

[zephead400ex]

Wrong forum, but I'll answer. Is it backfiring when you are accelerating or decel? If you are backfiring on decel, you are running lean, vice versua. You said you did these mods about 4 months ago...that was February. Weather has warmed, you are probably lean. Go bigger on the main jet.

[Chef]

Originally posted by zephead400ex
Wrong forum, but I'll answer. Is it backfiring when you are accelerating or decel? If you are backfiring on decel, you are running lean, vice versua. You said you did these mods about 4 months ago...that was February. Weather has warmed, you are probably lean. Go bigger on the main jet.

Warming up would make it richer, because the oxygen molecules arent as dense in the air.

[WOracing]

We just fixed it, we messed with the air/fuel mixture and now its running mint....thanks for all inputs:)