I would get the carb straightend out and make sure you have the timing correct before messing with the rings. I am pretty sure with a pro zinger and a can muffler that wasnt too restrictive that mine would turn 7100 with a zinger 18-10.. depending on now restrictive your muffler is you may not be that far off.. Are you sure some of the numbers guys are quoting are from running on glo?? They would turn 500-700RPM faster on glow than on gas.. Does your ignition advance the timing or is it fixed?