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Stuck Throttle or Lean Condition/Air Leak? NSFW - one curse word at end of video

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Been having what I thought was throttle issues lately with my 2005 YZ250. Totally disassembled everything from carb to throttle. Pulled slide, etc. Cable is new. Carb is almost new. Problem started recently. Nothing wrong with anything that I can see. 

So it finally hit me that I might have intermittent air leak, maybe a seal or something else. Not sure if a seal can leak and then reseal it self periodically.

What do you think? Can you tell anything from the sound? Check out light "stuck throttle" sound at 17 seconds, and then higher rev at 24 seconds.

 

Edited by LSHD

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Does sound odd, air boot, gasket seal on air boot reed cage, dry side crank seal, main bearing on dry side. Strange burbble sound at 17-ish. 

Have you checked the sealing areas mentioned, and I believe at different rev/RPM on crank, you can have an air leak that seals intermittent. 

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Going to pull the motor and completely check it for leaks, then do a top end while I have it out. Also been having a strange popping at just off idle that has gotten much worse lately. Jetting is perfect everywhere, so I suspect something else. This will at least give me peace of mind knowing she is air tight.

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I was going to do that (have done it before and have my own leak down tester), but it's a hassle with fittings while on the bike, and I really want to make sure everything is right. Might as well do it right once and not be second guessing.

This is why we have two bikes!

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1 minute ago, LSHD said:

I was going to do that (have done it before and have my own leak down tester), but it's a hassle with fittings while on the bike, and I really want to make sure everything is right. Might as well do it right once and not be second guessing.

This is why we have two (or more) bikes!

Exactly!!!

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I believe at different rev/RPM on crank, you can have an air leak that seals intermittent. 

Absolutely, I know this to be true. That's what I was thinking when I saw the video. Intake/reed is also a common spot for air leak but is usually more consistent.
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Thanks guys. Reeds are brand new and stock, and I had the same problem with the set I replaced. I checked reeds for leaks. Air tight. Seal is my best guess and will be replaced.

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When you had the carb apart, how did the needle and seat look on the float? It sounds like it's starting to run out of gas.

Is it sticking shut?

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Maybe do one thing at a time, crank seals are an easy replace. If that fixes it you know what it was. If not, topend and whatever else you were going to try One at a time if possible.

I have chased problems before that ended up to be crank seals. Different strange symptoms every time.

 

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Common problem on KTM Freerides. I have tons of info on another forum. Quick question, Does it always began on decel as the trigger.

 

 

EDIT: It is coming from a high vacuum on decel where the air rushing under the wedge shaped slide gets lifted, over powering the slide spring. To stop it, which is not the fix, but to keep it from happening on the trail, lower your idle as low as you can afford. This will miminize the air rushing under the slide. . A strong slide spring helps but not the cure. In the event that it happens while you stop, it will scare you to a panic as if the motor is about to blow. Lock the brakes, gear up and stall it dropping the clutch. The kill switch will not kill a run away because at that point, it is acting just like a diesel. 

Edited by 1gr8bldr

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5 minutes ago, LSHD said:

Just based on best guess, I would say it does tend to happen on decel.

I edited my last post rather than post again, but should point it out so you don't overlook it

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No help with your problem, but.. Damn, those are some open, fast trails. Doubtful I'd notice idle issues once out of the trail head parking lot. Pin that bitch and don't worry about it.. :thumbsup:

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Ha. That's about 2% of the trail. The rest is snaking deep sand with lots of tight turns. I chose that section because it shows the full range of throttle conditions. 

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