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1985 cr125 has a sickly cough

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i bough this 125 for a good price. clean and in sweat condition for an 85 mxer. the guy said it was just rebuilt and needed a carb tune. sweat no prob it will be easy. turns out it has been impossible to jet. i put a stock cylinder on it hoping the bored cylinder was causing the odd misfireing. nope not it. checked the reeds and they are perfect, all new gaskets so no leaks new plug and i read the plug after every test. i can get it to run good in the low end and transition to mid range but i can get it to run good through the hit range up to over rev. it just misfires on topend. i have got it to pull hard with one jet needle combo but only when it was not hot, 3 laps then it starts missing like its lean, and i will read the plug but it look normal. checked the float level and made sure it gets good flow into the bowl and not starving of fuel. the only thing left i can think on is the pipe. it has this odd pipe (the only non stock part other than the silencer) that is oviously not stock. it only has one mount tab. my qestion is this pipe making my bike impossible to jet or could i have cdi issues. weak spark is not the case cause it will give a good spark on a fouled plug and will start fist kick and idle forever.

some one with lots of cr expirence please help.

i will get a pic of the pipe tonight and try to get it up

thanks

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turns out it was a weak spark not jetting making the bike cut out.

i tested spark today for kicks. and what do you know it was almost non existent. pulled the harness connections apart they all looked good acept for one on the coil was pitted and was defininatly arcing. squished it with pliers and put it all back to gether, and bam my bike feels like a rocket. it even sounds differnt now, it dosent labor hard when you bog it and it revs to the moon. the weak spark realy confused me and i thought it was running lean but it was an electrical cut out not a fuel starve cut out. jetted it yet again now that the spark is working :bonk: and it pulls like non other but i will need new clutch plates soon... :naughty:

i hope my problems can help lead some one in the right direction to fix theirs.

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i bough this 125 for a good price. clean and in sweat condition for an 85 mxer. the guy said it was just rebuilt and needed a carb tune. sweat no prob it will be easy. turns out it has been impossible to jet. i put a stock cylinder on it hoping the bored cylinder was causing the odd misfireing. nope not it. checked the reeds and they are perfect, all new gaskets so no leaks new plug and i read the plug after every test. i can get it to run good in the low end and transition to mid range but i can get it to run good through the hit range up to over rev. it just misfires on topend. i have got it to pull hard with one jet needle combo but only when it was not hot, 3 laps then it starts missing like its lean, and i will read the plug but it look normal. checked the float level and made sure it gets good flow into the bowl and not starving of fuel. the only thing left i can think on is the pipe. it has this odd pipe (the only non stock part other than the silencer) that is oviously not stock. it only has one mount tab. my qestion is this pipe making my bike impossible to jet or could i have cdi issues. weak spark is not the case cause it will give a good spark on a fouled plug and will start fist kick and idle forever.

some one with lots of cr expirence please help.

i will get a pic of the pipe tonight and try to get it up

thanks

My friends KX125 is doing the same as you described, I'll let him know . Thanks for the post

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