Wont Rev, Misfiring....help

Ive been having some trouble with this pitbike I just bought. The guy i bought it from was having the same problem i am experiencing now. Idle's fine, starts to rev up, but it's abnormally loud, then it gets to a point where it just misfires, and backfires though the intake, and occasionally out the exhause. And if i open it wide open, it stalls. It seems to run its best, if you can even say that, with the choke halfway on...which would seem that it's running lean...i checked for intake air leaks, couldnt find any. When i first got it it was doing this, the guy said it started when he drove it in the rain. But when i brought it home, and adjusted the carb a little, it sprang to life and it couldnt have run better. but now, after riding it in extreme wet conditons yesterday, it is doing it again...i noticed that the intake gasket where the carb mounts on the manifold had some pieces that may have gotten down into the engine, like flakes almost, could my valves not be operating properly?...because ive done every possible adjustment to the carb, and its not doing anything...it has plenty of spark, good compression, and im assuming its getting gas since it idles fine. Something is making it run lean, or i'm thinking it may be a stuck valve, but it still may be an air leak... im stumped
what could it be?

i was told it was a takegawa, and its a popping loud, like its trying to rev but can't. Im pretty sure its not the carb, perhaps electrical?

im pretty sure it is the cdi box, it was filled with water when it wouldnt start. I dryed it and now it at least starts...he had the same problem after he rode it in the rain so it is most likely electrical if water affects it...ill get a new one and see how it runs.