cr 250 ignition problems

[fmfracing212]

just rebulit my cr 250 and it runs good until 1/2 throttle then its spark goes crazy.it starts first kick idles and wil have good power til 1/2 throttle.i hooked a timing light to it and it was showing good spark until i held the throttle steadily at 1/2 throttle then the light goes dim and blinks a little bit. i was wonderin if anyone has any suggestions what it could be thats causing the problem.
thanks jerrod

 

[energyrail]

what year

 

[DWreck]

His info shows it to be an 87.

 

[76GMC1500]

Your timing light probably can't flash fast enough to keep up with the spark when you're holding it at half throttle. Change the plug and clean the carb. If it runs good for a while and then starts cutting out at half throttle again, you may have a bad right side crankshaft seal. That's what mine did.