[jmudweiser]

2006 CRF250R,bought used, ran good but cold blooded to start. been out a few weekends riding and then only would bump start. As expected valves were tight. Re-shimmed, int @.006 and exh @ .010. I cleaned the carb wile down also. Now kicks over in the first 3 kicks. only runs w the choke on, or choke off w the idle set higher.My biggest issue is popping BAD!! Runs ok until letting off the gas, then lots of loud popping. if i loosen the mixture screw until its almost out it runs better.
I have a JD jet kit, new gasket kit, and exhaust gaskets coming in a couple of days. ive already been through the carb, super clean, only changed a slow jet from 45 to 40, just so i could start from basics to trouble shoot. Before adjusting the valves the pipe woould get so hot it melted the air box and would pop unless it was 4 turns out on the mix screw. i thought after the valves were adjusted this would fix it all??? whats the deal?

[sycraft]

Check for exhaust leaks....

[staffy24]

carb boot fuel screw o ring air leak ect

[crfsonly]

what made you decide to reduce the pilot jet size? the popping is generally a lean mixture and/or an exhaust header leak. check the header but the fact that you are able to improve the situation by opening up the fuel screw is an indication the pilot jet is too small.

[jmudweiser]

Sorry guys. When i pulled the carb apart i made sure everything went back to stock. That's why the #40 jet. Kind of a base line to troubleshoot. But i have since put new exhaust gaskets, rebuilt the carb with a JD jet kit, R&D flex jet, and shimmed the valves.
My popping was caused by the tight valves,and mixture screw missing its O-ring. I must say thanks to this site for its forum and parts support i have a happy kid with a bike that now runs perfect!so thank you to CRFSONLY.COM!!
-Justin

[crfsonly]

justin...glad to hear you found the cause and were able to fix it. thanks for the kind words.

ken