DT125 R Loses power at 7K RPM

i wouldnt recommend that an inexperienced mechanic could do this myself?

as for pointers

take out the oil filler...can you smell petrol?

smoke from the exhaust...is there lots of it that doesnr really clear when the engine is hot?

transmission oil level...is the level falling with prolonged use?

hi im having similar problems,i have a dt125r 2003,just had new piston etc,somtimes really smokey wen start it,sometimes spluttering at high revs 6/7k and the sometimes bogging in high gears but low revs,powervalve is in fully working order so is the air filter etc,could this be a problem with water in my carb as the weather hasnt been the best recently? or is it the crank seal,how do i check the oil filter? and my bike does clear out the smoke after just taking it down the road,thanks please help