If Im going pretty fast (100+mph) and I give the bike a good amount of throttle, doesnt even need to be WOT, It will stutter not accelerate and the rpm's will move up very slowly. This mainly happens in 4th and 5th gears (my bikes a 5 speed). Could it be fowled plugs not burning enough fuel causing the problem? or am I just in to high a gear for the speed Im going? By about 130mph Im pretty much stuck.

For those safety naizes out there: No I do not do this all the time, I wanted to see how ballsy the bike was once and now Im concerned there could be an engine problem.