question for the jetting experts

[nopulse95]

I know jetting is a trial and error thing, but any help will be greatly appreciated. I've got full white bros r4. 416 je 10.8-1, and hotcams stage 2. Airbox lid on and w.b. air filter. I've got a 160 main, 42 pilot, stock needle and position. Wide open it runs great, did a plug chop, and it looked good. It idles good, if i hit the gas while idling it doesn't break up. But when i'm cruising in second, and hit the throttle, it breaks up. I don't know if it's rich or lean, i moved the needle up, to richen it up a bit, and it seemed to make it worse. My problem seems around 1/4 to 3/4 throttle. Does my main sound too big, or too small, my pilot? Should I adjust air/fuel screw? Or should I move the needle down position from stock, to lean it out a bit? Also, i'm at 900' altitude, and it's about 65 degrees now...

[cals400ex]

i would run the needle in the 4th position from top. everything else seems good.

[nopulse95]

I have the needle in the 4th position from the top, it seems to run worse than in the 3rd positon. Thats why i was thinking maybe going the other way to lean it out a little.

[04'400ex'er]

Im not sure what you have done with the needle but 3 up from the bottom is stock, and I would move the clip down to 2 from the bottom.

[cals400ex]

yeah, i am not sure what the problem is either. my 400ex when it was stock actually ran better in the 4th from the top in the cold months of the year.

[nopulse95]

I took it out today, same setup as before, 160, needle 4th down from top, 42 pilot. airbox, a few small holes. I taped the holes up, and it ran worse than without the holes taped. So, i took the lid off, and low to mid was awesome. So, i'm rich on the needle, right? top end was bad with the lid off though. and top end was better with the needle on the 3rd clip. I know needle doesn't affect top end, so that confuses me. Could the colder plug, im running the 9 instead of the 8 cause a problem? sorry for all the questions, seems like after running for a while, it kept breaking up when i gave it throttle, like maybe dirt or something. could that be the plug getting hot? I have no idea what to do now?

http://www.atvriders.com/articles/sparkplug.html

[Fast350ex]

The pilot controls from 1/4 - 2/4 or 1/2
The main jet is from 3/4 - 4/4

[cals400ex]

are you running all keihin jets?

[nopulse95]

yes, all keihin jets. Since it ran good with the lid off in the midrange, i'm going to move the needle down, to lean it out a little, because I can't run without an airbox.