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My son's 2000 yz 80 just Accelerates uncontrollably. I cleaned the carb and it ran fine for a minute. Started doing it again shortly after. So I rebuilt the carb and it last 2 min longer. Now I'm stuck I think it's is the choke but not sure. ANY help would be appreciated.
 

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ZAMM Fanatic
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2,730 Posts
Personally I'd leave it exactly the way it is, put away your tools and get out your videocamera. Perhaps mount a GoPro on your son's helmet too. The resulting video(s) if posted to YouTube could make you rich. You might need to invest a few dollars in Imovie or some other video editing suite, and license a Heavy Metal soundtrack, but I can guarantee that'll be some footage his siblings will get a chuckle out of watching the rest of their lives.

In all seriousness, you need to take it to a motorcycle mechanic. If a loose throttle cable stop, broken housing, missing return spring, broken handgrip, or missing throttle butterfly isn't immediately obvious to you, then its unlikely you'll be the guy who's gonna fix this bike no matter HOW much bad advice you get for free on the Internet.

Be sure and use a tripod, and try and get a few panned "And the crowd goes WILD" shots immediately AFTER he motors directly into the neighbor's fence, over the dog, into the river or pond.... You'll have to write the script AFTER you shoot the footage, so try and emphasize safety, e.g. "Working on your own motorcycle, what could possibly go wrong???"

Looking at it another way; if your Intertube-guided throttle repairs don't hold and he's injured, you ain't gonna be getting any sex for months, even years. You really want to risk a stinkeye that lasts until the kid's arm comes out of the cast? Nope, there's a REASON why you want to pay a professional MC mechanic for his tools, knowledge, experience, and....blame-ability.
 

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Veteran Member
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My kid's cheap Chinese 70cc Honda clone did that. For me I found that the slide inside the carb was not sliding freely. The problem was a combination of a weakened return spring in the carb, and the crappy air filter letting in dust and hindering the slide. I changed out the filter and it solved the problem for the most part. But the return spring needs to be replaced, as it is still too weak. the trick is finding a spring that can return the slide reliably, but not be so stiff to cause throttle hand fatigue.
 

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Ghost in the machine
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I would remove the carb again. This time twist the throttle a few times and observe the slide to see that it operates correctly and not hanging up on the idle adjust screw. Also watch to see that the needle remains straight in the jet and is not raising too high and missing the jet when released. It is also possible that the float is not set correctly (just too low, or fuel IN the floats). 2 strokes often rev high when they are starving for fuel. They often do this just before you run out of gas.
I would also check the flow of fuel to the carb. A dirty petcock may be restricting the flow causing the starving / high rev.
And while you have the carb off, clean it again.

Hope this helps. Let us know what you find.
 
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