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xr 250 ignition problem

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I was wondering if anyone has had any problems with elect. components on their bikes. I just rebuilt my eng and can't get it to run right, at first I thought it was a fuel problem but after cleaning my carb twice, setting the float level three times and jetting numerous times, no luck. Jetting is 42 pilot, 122-128 main (no difference). It starts right up, but pops and misses at midrange and top end and soots up the plug. It has good compression, valves are set right, and valve timing is on. Sometimes it runs great but has a slight miss and puffs black smoke, only to foul the plug half hour later. I just replaced the coil and plug cap. I've got the Honda manual and everything is testing fine. I checked my pickup coil air gap last night only to find it its right on and not adjustable. I'm wondering if it may be my CDI unit, theirs no check for this in the manual. I bought the bike not running, so I don't know if this was a previous problem or if something may be out of adjustment or gotten broken during the rebuild. I'm starting to run out of ideas and the Honda manual isn't helping me anymore.

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sorry for the late post.

But i had Coil problems, the previous owner had jammed an oversize or worng plug in the head (eventually fusing it to the head) and the coil was woring overtime trying to jump the gap.

Mayeb double check the valves?

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I had much the same problem when I first purchased my bike. The engine wasn't missing but I couldn't solve the fuel richness with jet changes. I checked the resistance of the impulse generator, coil, and plug cap per the shop manual and found the cap had WAY too much resistance. A new cap solved the problem. No need to change the coil, just the cap at the end of the wire.

Dave

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Just wanted to update you guys on my progress. I just replaced the coil and cap with new aftermarket, swapped out the CDI unit and crank pickup, all with no changes. The valves are good, I'm going to pull the valve cover off tommorrow and double check timing. I'm wondering if the flyweel could have lost some magnatism, the generator coil tests good.

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