I have a 2001 400ex with a Pro Circuit T4 exhaust, 7, 1" holes in the airbox lid, K&N filter, O/W, stock gearing. I've tried a 160, seems a little lean, have 170 now, seems rich. Heard different people recommend both???

 

I'm curious as to how you made those determinations as to rich or lean...did you do test/plug reads or was it an impression of the performance? If you did take a reading on the plug after a full throttle test and each showed incorrect jetting with those two sizes, who not split the difference with a 165 main and re-test?

 

I checked how it was burning by plug checks, exhaust checks and performance. I tried those two sizes by looking at what others were recommending. I know that there are choices in between, I was just wondering if someone had tried a bunch of different ones and really dialed theirs in. That's what I still need to do, just looking to take the lazy route. Thanks for the feedback

 

My dynojet book said to run a 170 with no lid and a 146 with a lid. This seems outragous because stock is a 148 but they are exactly right! It ran the best when I did exactly what the manual said, that was with a different needle and the air screw 3.5 turns out.