Hi by copy I mean it is a SIKK engine it is brand new I have removed the flywheel and mag replacing it with a ZDZ ignition unit and a slightly different walbro carb. The exhaust is a standard unit with the guts ripped out and a larger outlet pipe. I have also tried it with a MVVS tuned pipe and it makes no difference. I dont think that there is an external limiter but I do still think that it is a port timing issue. But I am open to being proved wrong.
Regards John.