i have a very beautiful 2004 kx125, i picked it up a few months ago and when i got to the guys place to check it out, he started it by foot like normal and i rode it around the yard and about 500 feet i went and brrrrrrrr it fouled the plug??? but it was 1800$ so i was like heck with it im still getting it to the looks of the condition and claimed recent rebuild. i took it home and we replaced the spark plug and we had to bumpstart it this time. again 500 feet and brrrr fouled. this bike has a BRAND NEW mikuni carbourator OEM with jetting and airscrew position on point, Timing is perfect, i even tried advancing and retarding the timing, still nothing. i put it back in its normal position though. Reeds are good. no gasket leeks. good compresion. spark plug is BR9EIX NGK. it gets a spark, its getting gas, its getting air. when i try and start it, it back fires sometimes a loud pop. carb should be out of question, timing should be out of question. what else is there to check? i have talked to a few people saying it might be either, crank seals, or the stator. but i have NO IDEA of what to do. please help me i know u guys might know what to do, im 15 and trying to get into mechanics and i try to be the best mechanic i could possibly be with my hard earned tools. 4/1/17 ill be checking on any comments or suggestions every 8 hours or so. and i also dont want to buy new parts for the bike that it doesnt need. Thanks for reading! give me your best shot, I accept any help!