I have a 2000 honda 300ex and when i rev it up high it blows black smoke i have a fmf megamax exhaust. before this my carb was messed up we rebuilt it exccept for the jets the carb would flood out before we rebuilt it.it also blows out blue smoke if you top it out and then let off the gas i dont know what is wrong with it does anyone have an idea

 

Sounds like your valve seals are going, when you let off after revving it out on top end, it creates a vacuum that pulls a tiny amount of oil past the seals into the combustion chamber,burns and give you blue smoke. When they get bad enough, it will puff blue smoke on start up after sitting, then not smoke unless you rev it out.
Black smoke when revving is running rich, either your main jet is too big,the needle is set too high, or your float is still off, allowing too much gas to be sucked in at high rpms. Go through the carb, make sure float settings are right, you may need a new needle and seat, check jetting and jet needle settings, you should be able to get jetting recomendations from the FMF web site. The blue smoke means a top end gasket set with valve seals,if you are taking it apart, good time to check compression and see if it needs piston and rings while the top end is apart.

 

thanks for info it is bored to a 349cc too

 

holy crap! haha. may i ask, whats all done to this thing internally?

 

im not sure whats all done to it internal . its got lots of power probably more than a yamaha warrior its a beast. i didnt bore it and stuff. the guy who had it before the guy i bought it off of did it but its sweet