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06 YZ250 bouncing idle.

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Just recently my bike started idling weird. It has done this in the past few weeks, but usually went away when I either: adjusted my air screw and let it warm up more, or left the choke on for a bit longer than usual. I can get the idle to even out by lifting the choke, but once I begin to rev it again, it will have a "pulsing" idle upon decceleration..

Does anyone know what might be causing this? I plan on going into my carb this week to go up one on my main jet because my plug is looking kind of lean and it's beginning to get colder where I live.. So if you guys can give me a check list of things to do or look at while I'm in there, I'd appreciate it.

Extra info that might be useful:

Pipe: FMF Factory Fatty

Stock Jetting

Mixing Maxima Castor 927 at 32:1 with 91 octane gas

Elevation: Varies between about 460 and 520 feet above sea level depending on where I ride at.

Edited by Rider of the Plague

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First of all, I wouldn't judge jetting when you have your choke on. Also have the engine up to operating temps.

If you have stock jetting, you are likely to rich on every circuit for your altitude. I'm around 1500ft elevation and have 175, 48 and 2nd clip. But there's to many variables to say.

I also would ONLY mess with the pilot jet on the stand. The rest of the circuits need to be fine tuned with the bike at operating temp and being ridden.

If the idle is bouncing after you let off from 1/2 throttle, move your needle clip.

If the idle is bouncing after a full throttle run, adjust your main.

etc..

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First of all, I wouldn't judge jetting when you have your choke on. Also have the engine up to operating temps.

If you have stock jetting, you are likely to rich on every circuit for your altitude. I'm around 1500ft elevation and have 175, 48 and 2nd clip. But there's to many variables to say.

I also would ONLY mess with the pilot jet on the stand. The rest of the circuits need to be fine tuned with the bike at operating temp and being ridden.

If the idle is bouncing after you let off from 1/2 throttle, move your needle clip.

If the idle is bouncing after a full throttle run, adjust your main.

etc..

Thanks for the response. I forgot to include that it did this when I was riding this weekend, and not just when I started it at home. Should I go up on the main or move the needle up? By the way, here's a couple pics I snapped of the plug about a week ago while I had it out.

2r5w800.jpg

1gncir.jpg

I looked at it again last night and it looks pretty much the exact same

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Thanks for the response. I forgot to include that it did this when I was riding this weekend, and not just when I started it at home. Should I go up on the main or move the needle up? By the way, here's a couple pics I snapped of the plug about a week ago while I had it out.

I looked at it again last night and it looks pretty much the exact same

Does the idle surge or is it blubbery?

Looking at those pics, the jetting looks fairly close. I would verify what circuit (needle, main or pilot) is causing the pulsing.

I'm going to bet though, if you moved the clip down one position from the top of the needle (richening mixture) it will cure it.

But I'm guessing you are describing a lean mixture.

The good thing about going richer with your jets, if it is the wrong way, it will get worse, and you know you weren't lean.

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Does the idle surge or is it blubbery?

Looking at those pics, the jetting looks fairly close. I would verify what circuit (needle, main or pilot) is causing the pulsing.

I'm going to bet though, if you moved the clip down one position from the top of the needle (richening mixture) it will cure it.

But I'm guessing you are describing a lean mixture.

The good thing about going richer with your jets, if it is the wrong way, it will get worse, and you know you weren't lean.

I guess you could say it pulses. When idling it will sound like: duh dun dun...dun...dun.. duh dun..dun...*rev* duuuunn..dun..dun... :busted: Haha it's hard to describe, hopefully you know what I'm talking about, though. It just will not steady itself out.

I think I will try to move the clip down one tonight and see if that helps. Hopefully it will go ok considering the only carb work I've ever done was swapping the main jet my old '98 yz250. These carbs on the newer model YZ's are much more complicated with the Throttle Positioning system and everything.

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Alright, let me give you an update:

I took the carb out of the bike.. cleaned the float bowl, main jet, and pilot jet with gas and then blew the jets out with compressed air as well as the float bowl. There was a tiny bit of dirt on the intake side of the carb, but I made sure to wipe everything down pretty good. I got everything back on the bike and decided to give it a little start up, even though it's 11:00 here :busted:, and it idled great. I didn't really get to rev it much for obvious reasons, but I did rev it kind of softly and it didn't sound too bad.

I don't know if it's significant or not, but when I started it up, the air filter was off for cleaning.

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Most of the time when winter comes around the idle on my bike starts rising. Also when I rev the bike it takes too much time to come back down to idle. That's when it's time to put in one size bigger pilot jet. The bikes running lean in when it gets colder out. If the symptoms get better when you screw in the air screw then you now thats the issue.

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You might take a look at you reeds. Still stock? Inspect for small cracks. I had an old 2smoker that developed a surging idle and that was the problem. May not be in your case but worth a check. :busted:

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