Hi Steve,
I have the same problem, check out the solution I am working with here:
http://stunthanger.com/smf/index.php?topic=20796.0
My tests with this carb mod are not complete yet but I have the Wasp up to 16,100 rpm on a 6-3 Master Airscrew prop, although after more than 40 minutes of break-in, the engine is still tight and won't hold the max. rpm.
Orv.