Jetting help - stock 07 yz250f.

Well, I got my bike the other night, and got to really ride it today, and noticed it is really popping off throttle and even on the throttle to a degree. The bike came with 2 extra main jets, a 175 and 180. What should I do to richen the fuel mixture up? Do I need to change the clip position on the needle or anything? My riding is at around 2500ft, under 10% humidity and in the mid 70s right now. Thanks.

I would change the needle position first and work from there

Needle posistion has nothing to do with popping on decel. Why? The needle doesn't even control that circuit!

Very slight popping indicated that the fuel mixture for the pilot screw/jet are set. Backfiring out of the exhaust indicates too righ, and you should go in with your fuel screw. If you are in less than a turn, richen your pilot jet one step, and then adjust. If you are more than 2.5 turns or so out, go down one step on the pilot jet, then adjust the screw acordingly.

Backfiring into the carb/airbox indicates a lean condition (sounds like a machine gun from the exhaust). You can hear this condition easier with the seat off. This will mean you should go out with your fuel screw. Read above to choose the pilot jet.

Note that the pilot jet and fuel screw do the SAME exact thing. The pilot jet determines the number of turns out. So if someone claims "just go bigger on the pilot" in essense, just go out on the fuel screw. If you are still between 1-2.5 turns out from seated, there is no need to change the pilot jet.

Having a larger pilot will mean you will have less turns out on the fuel screw, and a smaller pilot jet will mean you will have more turns out (in the same conditions)

Cool, thanks for the info... It sounds like a machine gun enough that when Im off the gas and slowing down, Im just pulling the clutch in to shut it up.

Pull your seat off and ride without it. You should clearly hear it through the air filter.

Go in increments or 1/4 turns out on the fuel screw. When you get the sweet spot of a pop or two, count the number of turns out...

I was just going off what i did to my bike when it was running lean and it helped with popping but when i changed jets it made it run to rich but you sound like you know what your talking about more than me

I was just going off what i did to my bike when it was running lean and it helped with popping but when i changed jets it made it run to rich but you sound like you know what your talking about more than me

Just because it worked for you, does not mean it correlates to the OP's problem...

Just because it worked for you, does not mean it correlates to the OP's problem...

Dude chill out i wasnt being a smart ass or anything you really do know what your talking about more than me and i do realize that not everything works for everybody, it was just a suggestion

So to be clear, I shouldnt change the main jet from the 178 to the 180 supplied in the pack with the bike, even though its running lean? Also, what does the manual call the fuel screw? Is it the jet needle, and where do I adjust it from? (I suck at carbs, but need to learn this stuff)

So to be clear, I shouldnt change the main jet from the 178 to the 180 supplied in the pack with the bike, even though its running lean? Also, what does the manual call the fuel screw? Is it the jet needle, and where do I adjust it from? (I suck at carbs, but need to learn this stuff)

You should read secion 7, primarily pages 1-10

What you are looking for primarily is on page 7-3, which will answer your question about the main jet. Notice the openings and the effects of each. Usually the "throttle valve cutaway" doesn't get touched...

The screw is listed on page 7-5. Refer to it as a Pilot Screw. It is located on the engine side, way up there. You may have to buy a attachment, a different fuel screw that is extended, or use a bit attachment for a drill (just a flatblate). You can also rotate the carb out towards the left side to get easier access, but you must turn the motor off, and can be time consuming.

Alright thanks

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