outssider,
MT warranty work is handled out of their Florida office,
www.MTEnginesusa.com. They have been noted for responsive customer service, so try them if Larry can't help you.
A flaky ignition can cause some weird behaviour; I've had one RCExel on a different brand replaced under warranty, with much better results than I expected. It can definitely affect top end rpm & power if it's even a little marginal.
In addition to checking your battery and plug gap as Dick suggests, you might try using a different switch between the battery and the ignition as an experiment. Also the spark plug cap takes pretty firm pressure to seat properly and I've had trouble with those before. One other thing, is the magnet for the ignition sensor passing fully under the sensor? I've seen a case where the sensor couldn't get a reliable reading on the magnet because it wasn't properly aligned.
Good Luck!