[24NateFrye]

My 2002 trx400ex goes 1/2 throttle or 3/4 and then it bogs out. Sometimes it won’t even let my give it any throttle. I took the air box lid off and it helped so I put some holes in the lid. But it still did it after a little. Then I took the jets out and cleaned them. Could there be an adjustment on the carb or something? Could it be getting too much/ not enough air? Plus I just did a top end rebuild and it is a 426, so should it be ran on high octane? Or should I just buy a whole new carb becase they are pretty cheap. I don’t know what to do so any help would be greatly appreciated.

 

[SamUK]

So you've done a over size bore and assume that fuelling will be the same as stock.....??!!!!!!

Have you changed any jets in the carb? Have you changed the pilot jet (air fuel) mixture screw?

More importantly, have you looked at the color of your spark plug?

 

[24NateFrye]

I just bought the fourwheeler not too long ago so i don’t know if the jets are changed but it ran before I took apart the top end. It was bored when I bought it off the guy. I will buy some new jets and screw to appropriate size. I will also look at the spark plug, it looked fine before but I will check again. Thank you, if I have any more problems I will say.

 

[24NateFrye]

So I looked, my spark plug was horrible, and do you happen to know what size jets I would need?

 

[24NateFrye]

Sorry the spark plug is all dark black.