my sons drx 90 air-cooled flies around the track and then he goes to turn right and loses all power and it bogs down and ends up at the back of the pack. i've tried rejetting, different rollers, bypassing the pekok. any hints would be great.  

does it bog only when he turns right?

if so then you most likely have a short in a wire in close proximity to the steering shaft/handlebars.

i had a blaster that would die if you turned the handlebars to the right.  pull the cover off and look at the wires as they run around the steering shaft and handlebars and make sure the wires aroun't binding.

sometimes the throttle cables will bind there too and it pulls the cable housing out of the top of the carburetor causing an air leak in somne carburetors.