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ZY80 (yr2000) slight stumble @ 1/4 throttle

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I recently purchased this YZ80 for my son and noticed the engine stumbling thru 1/4 to 1/2 throttle. Runs great at all other throttle positions.

Yeap, I'm am new to the 2 stroke engines.

So I did some research and found that the Needle jet controls 1/4 to 3/4 throttle.

Note: this model has 5 clip settings on the Needle.

I found the clip setting at the 2nd highest position on the Needle. So I re-postioned it to the highest setting, therefore lowering the Needle to the max.

This helped out quite noticeably, but it still has a slight stumble around 1/4 throttle or so.

Is this condition inherent in the 2 stoke designs? Could this be an expected condition considering its a 10 year old bike?

The bike is good shape and runs good with expection to this stumble, and it's more of an annoyance factor. Am I asking for too much?

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