I ran it some more today on a different muffler. A solid 7770rpm today. This is a Hatori heli muffler for the G-23 that I've had laying around for about 10 years. Large volume, a lot less restrictive, but still very quiet(wouldn't fit too well on most planes though). I knew this motor was going to respond to a muffler change, still on the stock carb and air filter. The stock carb is great for running on the test stand as you can put the throttle anywhere you want and it will hold that position. None of the B&B type mufflers that I have will bolt straight on, but anything designed for the G-23 can be made to fit with some moto-tool work (bolt hole spacing is a little less) I've got a heli header (that I've already modifed to fit) and V-Tech tuned muffler that should give a big boost in horsepower that I'm anxious to try after I get a little more run time on the motor.

Pics still won't upload, I've got to find out what the problem is.