possible elecrical problem

i have a 99 yz 250
fresh topend
full exhaust
vforce reeds

the problem im having is
if i put a brand new plug in my bike i can usually ride all day.
if i stop riding to take a break and let the bike cool down and then start it back up i can ride 1-3 minutes and it will foul a plug(wet and black sometimes sootie)
or
if i ride all day on a plug the next time i ride ,like the next day, i do a cold start the bike will run for about 1-3 minutes and then it will foul a plug. (wet and black sometimes sootie) if i put a new plug in it after that the bike will run all day again
i also am having problems with the bike loading up at low rpms and missing at top end

does this have anything to do with electrical or would it be jetting or my floats

im runing the stock plug br8es/br8eg tried a br7es but it fouled too