Scooterotica

here`s the situation, ive got a gp with a jb tuned muggy 186, 28mm del orto breathing through a foam filter and out through a jl3 curly. It was dynoed at 17.4bhp at 6569rpm and 14.2 ft/lb @ 6280rpm, but i melted a piston almost imediately, so i retarded the ignition, up jetted and didnt ride it much. Now although its not as sharp it still flies but it now seems over geared (tv175, 15x46), and especially the gap between third and forth is hard to span.
my options are different (lower) gearbox, sadly a 5 speed is out, or somehow widen the power band, any ideas without loosing too much more umph or spending too much, would an augusto type device help for instance?

The exhaust is something you could look at too. It could be it's pushed the power too high up the range and is struggling to find it..... Or something like that.

Easy. Take top end off.. Sell it.. replace it with a GT top end.

You'd be better off with no higher than 5.0 final drive ratio. LI150 16/47