Ever since the temperature has been dropping outside, my 01 yz250f is doing something wierd. When i hit the throttle and let off, it still seems to stay up in the rpms until i quickly blip it again and it comes to a normal idle :cry:. My throttle isn't sticking or anything, that is all working properly. I remember with my r/c cars, if the mixture was too lean, when letting off the throttle the car would continue to coast and rev until blipping the throttle again. My guess is that since its getting colder, the carb is getting leaner? It also pops now on decel as well. I guess I will try backing the fuel screw out a 1/4 turn at a time. As far as this throttle/idle issue though, what do you guys think it is?

You've diagnosed the problem exactly right. :cry: The cool weather makes for more dense air, leading to more oxygen in each gulp of air through the carb, making you a little lean. This leads to what is commonly called a "hanging idle", and some popping on decel. Opening the fuel screw in 1/4 turn increments will solve the problem.

With ever-cooler temps as winter comes on, you may find it necessary to drop the clip one position, and you might go up one or even two on the main jet.

Bingo. Nailed it right dead on.

Just for the record, popping on decel is a lean condition, while backfiring is a rich condition. :cry:

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