hey i am new to the site and to atv's..... i just bought an 02 honda 400ex and its not running right. It's not that hard to start but when it does it seems like its not idling right like it doesn't sound fluent. Also when i rode it the other day when it got warm it would shut off or stall when the clutch was held in. Then it wouldn't start until it cooled down. then when started again it sounded like it backfires, or pops, misses I'm not sure. i looked at the plug and it was black maybe just carbon fouled? the quad does have an fmf slip on and k&n air filter with no lid the jets are 152 and 38 im down here in Florida . i also took apart the carb (this is how i found the jet sizes out) and cleaned it still runs bad though. If anyone can help me that would be great

 

Does it have a performance cam? Was it raced? Cleanthe carb again. If no help, take a look at the valve adjustment. If good, take a look at the rocker arms. These are all easy things to do.

 

no it doesn't have a performance cam... it might have been set up to race a little bit but I'm not sure since i just bought it like a week ago... and I'll take a look at the valve adjustment and rocker arms.

 

If it's missing at idle, it's a pilot jet adjustment or clog. If it is missing at speed, it's a main jet clog or problem.

 

Ok well the pilot and main jet didn't looked clogged... so am i running the wrong sized jets with just those two mods mentioned? also the fuel air mixture was set to 2 1/4 turn out. and I'm not sure if its missing at idle but it doesn't sound right.... but at speed and deceleration it seemed to pop and stuff.

 

Yeah, check the jet sizes. Is the air filter clean?

 

the air filter is clean and the jet sizes are 152 and 38