My sons KDX started to lose power in the upper range of the power band this weekend. Had been running great but it just started to surge under acceleration and would not idle. Screwd out the idle screw and it will idle but takes seconds to fall into an idle, will slowly idle down .Anybody have any ideas that I can check out? Am baffled because it happened so suddenly.
Just a guess but maybe your exhaust valves are clogged. I know this can effect the performance at high RPM's in the powerband. I recently re-built my top end and mine were almost completely clogged up.