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MXRICH MXRICH
6/17/2018 7:12 AM

My son's Yz125 won't rev out and breaks up at 3/4 to Full throttle. This unfortunately happened at the all-star race at high point. It ran well without the humidity, Lowered main to 400 and raised clip to top on needle. It got better but still wouldn't go. Any help would be appreciated.

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kb228 kb228
6/17/2018 9:44 AM

Im sure its jetting related because of the humidity you mentioned, but i have seen bikes not rev out due to a bad plug or incorrect plug gap.

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BobPA BobPA
6/17/2018 7:23 PM

What exactly is it doing?

Tomac and/or Anderson for 2020.....

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chillrich chillrich
6/17/2018 8:29 PM

Open resistor spark plug cap will do this. Should measure about 5k ohm when removed.

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MXRICH MXRICH
6/18/2018 4:46 AM

Bob,

Builds and sounds crisp until I put it full throttle, then it breaks up.

Chill,

Gonna meter all ignition now.

Thank You

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MXRICH MXRICH
6/18/2018 11:42 AM

Went through ignition specs. Only out of spec reading is primary ignition coil. Spec is .24 -.36 OHMS. Mine is reading .5 ohms. What do you think?

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kb228 kb228
6/18/2018 12:57 PM

Sounds like you got a bad coil. Too much resistence for a supplied voltge will result in a weak or no spark

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chillrich chillrich
6/18/2018 4:50 PM

Had the coil do the same thing on a KTM105SX. Hopefully you have buddy with a YZ125 so you can try it b4 you buy one.

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MXRICH MXRICH
6/18/2018 5:07 PM
chillrich wrote:

Had the coil do the same ...more

I don't but i'm going to clean off the contacts on the coil and ground and see if the reading changes.

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