Am I jetted wrong?

[MITrail400EX]

I went riding this weekend after installing my new-to-me E-series slip on. I noticed that any time I went above 3/4 throttle with any sort of load, the motor would sputter, spit, and do everything except go faster. I haven't had the plug out to read it yet, but I have a feeling that my main jet is too small. I'm running the dynojet stage 2 setup with the 165 main installed. heres some specs and I'm hoping someone who is running the same basic idea will tell me what is wrong. Thanks in advance.

2003 400EX
Air filter: K&N with outerwear wrap
Snorkel opened up at the intake end
E Series slip on with 8 discs in (took 4 out for sound purposes)
Carb: Dynojet re-jet kit, stage 2. 165 main jet, dynojet needle on #3 groove, fuel screw 3 turns out from closed.
Spark plug: stock plug/ heat range
Altitude: <150ft above sea level
Sometimes I ride with the airbox lid off, not this time though. SOMEONE HELP ME!!!
:confused2

[MITrail400EX]

Just bumping this up so maybe someone will read it.:blah:

[ZSK]

By spit and sputter it sounds like you were running rich, usually it will backfire it it runs lean. Try taking the airbox lid off and running it to see if the problem still happens, deffinately check the color of the plug. If anything get a couple new plugs and start going through your jets.

[cals400ex]

check your plug first. i also say your too rich. a dark brown or black indicates a rich setting. many people disagree with me and put in a dynojet 170 or so when they have a pipe. i don't agree. i would put in a dynojet 152 or so. i have a complete sparks x-6, no choke, uni air filter, and no air box lid. i put in a 165 at first and it was too big. i went down to 160 then to 158 then to 155. i had increases in power every time i rejetted. when i had the 165 in, i actually had less power than i did when i was stock. good luck