Backfiring at start up?

[TRFOXX]

Hello, I have a 01 400ex with an FMF powercore IV slip on, jetted at 152 main and 4 - 1" Uni vent holes in the air box, with a Uni filter, stock pipe. I check the plug often and its the right color. The machine runs like a beast! But when cold and during warm up its backfiring? When she's warm/hot she stops and it dosent do it anymore at all. Im not lacking power and the spark plug looks good, I dont have any motor mods. My jetting is a little low compared to all you guys but I dont have the motor mods like you all either though. Dose she need more or less air through the air box? I really hate to mess with the jetting when she running so fine and the plug looks right. What to do? Need a little help?

[JabberJaw]

I have that same problem when I get up in the morning!!!

Actually, that sounds normal. My bike is stock, and it will miss when its cold.

Try turning the idle mixture screw out 1/2 to one turn more, it might help.

[Atomic83]

when i started mine last weekend it would crank and i would try to keep it running and then it would backfire really loud. sounded louder than a gunshot. i messed with it for like 5 minutes before i got it started and running good. today i went to my dealer and ordered a #40 pilot jet. hopfully that will help.

[barbwire44]

I had the same problem when i installed my powercore IV, it would backfire on start up and had a slight miss at low rpm when warm, I had a uni filter and six uni vents. This is what i did to remedy the problem 152 main jet, #40 pilot jet and raised the needle one position(lowered the e clip 1 position). This solved the miss and it ran even better.If you dont get a bigger pilot jet definately raise the needle i did all my carb adjustments seperately and when i raised the needle it stopped backfiring and missing but the larger pilot does help the cold start problems. Also being from ohio the altitude should be close, and i would definately think this will fix you're problem.:D