400ex low rpm miss????

[barbwire44]

I have a 01 400ex, After i installed my fmf powercore IV-2 the bike has a constant miss at low rpm sometimes it will stall completely when held at a low rpm. I tried rejetting i went with a 40 pilot and a 150 main which fmf suggested and it didnt help so i tried a uni filter and some vents in air box still no luck i re- adjusted the valves and still misses. I called a couple shops with no luck they suggest bringing it in but i would rather not. any ideas??
Thanx

Does it still do it after it's completely warmed up? My studders a little while it's warming up as well, when I give it a little gas and try to hold it there. After it warms up though it runs fine.

[Red Rooster]

try a #42 pilot jet my 300 had the same prob. and that fixed it :devil

[oynot400]

What type of gas are you running? I ran some lower octane gas on the trail (only because that was the only gas available) it would run real crappy exspecially at lower rpms. I have been running cam 2 (the blue stuff) for the racing season, now I have been mixing it with 92 octane about 50/50. That seems to work well for trail riding.

[barbwire44]

The bike misses wether it is hot or cold it doesn't seem to make any difference, as far as gas goes i run 92 to 94 octane and have tried different brands and also tried some klotz octane booster it didn't help either.
thanx

[barbwire44]

One more thing while were on the jetting problem. I know a lot of guys who have put the k&n kit in and had good luck but it doesnt change the pilot jet just the main and needle. Im starting to wonder if this isnt a needle problem.