This is a long and kinda complicated post so if you know what your talking about, please read!!!!

Alright so I just bought an 02 400ex from a guy who used it for racing. The idle was turned off so it would die quick if he fell off, and it has a white bros exhaust on it. Being an idiot, I thought I should turn it back up so it idles quicker. It worked fine for awhile but now whenever I have the choke off, it dies, even if it's warmed up. I've now tried every idle setting (turned it all the way down and turned it up half a turn, waited for it too die after I put the choke off) I think the carb might have got dirty from all the extra air coming in but I'm not sure and don't want to take it apart if I don't have too. I rode it with the choke up half way, but when the rpms get too high it sputters and if I put the throttle up all the way it dies, but when I ride with the choke off, it backfired even more Help!

 

Clogged pilot jet, the carb. needs to be cleaned

 

thanks ill tell you how it goes

 

Which screw are you adjusting? There's a screw that adjusts the mix (pilot screw) and a screw that adjusts the throttle stop. It sounds to me like the pilot screw either needs adjusting or cleaned. But even then, you have to work both screws in order to get the idle right. Mix first for smoothness, then the stop for RPM, then back to mix, then stop again. Look in a manual.

 

Thanks I'm downloading a manual now

 

The only thing I adjusted to make the idle faster was the idle stop switch, I never touched anything else before it stopped working right so why would I need to turn with the mix screw? Does the idle stop switch effect anything else, and would I have to tune everything?

 

The idle stop screw doesn't affect mix. All it does is the same thing you do with your thumb. If your pilot screw (mix) is in the right place according to the manual, + or - a 1/2 turn or so, and it still doesn't run right, I suggest you remove the carb, carefully disassemble it paying attention to where everything goes, clean all the parts and ports with carb cleaner and compressed air, maybe a pipe cleaner if necessary, reassemble and see if it helps. Oh, and make sure the tank has fresh gas and make sure the air filter is clean.