idle

[doubletimebluz]

My 2009 450 XC W is having idle issues. Ive looked on the site to see if anyone else is having this trouble, but cant find an answer. Bike has a FMF Factory 4.1 pipe. With choke, bike idles high for a bit,like it should, then races. When its hot, choke off, bike idles ok till you touch throttle at which point it races, only option is to hit kill switch or bump in gear and let out clutch to bring it back to idle(sometimes kill switch is only option). Bike will crank right back up and idle till throttle opened a bit. Bike will ride ok, once rolling, racing idle tends to go down to normal. Any ideas?

[tye1138]

Very common problem, I'm kinda shocked you can't find an answer.

Excess air is what causes the motor to run wild on its own, so that can be caused by many things. Sometimes its a crack in the boot from the carb to the motor. Sometimes its a carb issue with the idle screw, air jet or throttle plate itself getting stuck open somehow. I've also seen poorly routed throttle cables causing the same problem and its racing because the cable is taught and its opening up the throttle plate on its own.

I'd check over all of those things and see what happens.

Remember this, carb's work through vacuum build up and that means when you give the engine more air, it starts to rev more and then suck more and that sucking feeds it more fuel. So its a never ending sequence of events that leads to a motor revving out of control...