Heres my scenario.

05 400EX. took airfilter off last week to clean it. 2 days later, reoiled and installed and was running strange. then wouldnt run again unless i put the choke on. if i had the throttle going and switched the choke off it would shut right down. i knew it had to be dirt in the carb...no rain was killer on airfilter so that didnt help with airbox being so dirty.

Saturday i was determined to get it going so sunday i could ride all day. Went and bought a TwinAir filter and a new plug for the hell of it. installed everything and still no good. i have ruled out fuel since 4 quads have ben using the same gas for over a month now. today i took the carb out and dismantled and cleaned everything with carb cleaner and reinstalled. Seemed to run better. kept revving it and exhaust was kinda white...then once headpipe got pretty hot and bright red i knew it was running rich. now its 10:30pm and i run out to the garage and take carb off after reading owners manual and said that if you are at higher altitudes that it will run rich and it could be adjusted. there is no external screw for adjustment. just idle and fuel/water dump. i took the bottom off of it and noticed that the jet seems adjustable in the way of being deeper or more shallow into the carb.


Any one have suggestions? I am at a loss here and honestly dont know much about workin on tese motors, I was a car guuy until now!

 

Sounds LEAN not rich to me (runs better with choke on, runs hot, white exhaust, etc.), like maybe you have an air leak somewhere in the intake (it's getting to much air for its jetting). Is the intake tract a little dirty inside (wipe it inside with a clean white paper towel) , like it is sucking dirty air from a leak somewhere? Is the plug light in color or even white? And, the new Twin Air filter should make it even more lean, as it flows more air than a stock filter.

Check things like the crankcase vent for leaks (cracked hose, etc.) and that the intake boot is sealed. It's easy to test for a leak. Just take the air filter off and turn the engine over just slightly (with the kill switch on) while holding your hand over the end. It should create a vacume and it should hold that vacume if there isn't any leak.

 

Your absolutely right. I was talking to a friend today about it and he said lean and made me do more thinking. i dont know what would make it lean. airfilter is on tight. clamped everything down good. should i change the jet size up a size? i do have a jet kit i was holding until i got an exhaust. what else is there to do?

let me know what you think and maybe tomorrow ill bump the jetsize up

 

If it began running lean for no good reason, that suggests a leak in the air intake tract.

 

Heres what i encountered today.

installed dynojet kit with smallest jet and needle. was running rich.

Reinstalled stock jet and was running rich.

reinstalled stock needle with stock jet and running lean.

i am really getting pissed off with this now. there is 6 different settings withi the needle and i had it at 3. i think i am going to put it on 1 and hope it will be sufficient.

i tightened down all screws to intake so it was sealed and no luck.

The dynojet kit shows a pic with a fuel mixture screw but on my carb it is just a brass screw with a flat head in there and i cant adjust it. the kit says 99-04 and mine is an 05. that could be a problem.

 

New plug is black and burnt a bit. not too far off from my original plug.


any suggestions??