I also took the trimmer head off and turned the engine 11,000 briefly to make sure the coil/magneto was not RPM limited. It easily would have turned 13,000 with no load.

Notes for the Ryobi that I am converting:

The Ryobi will turn 7500 and occasionally touch 7600 RPM with small Bennett muffler. The muffler is fairly loud.

The Ryobi will turn 7600 occasionally touching 7700 RPM with open exhaust.

Ran it with the air box off and it appears to drop a couple of hundred RPM.

First run. Box stock air box and muffler. 7200 RPM. 16x8 MA prop.

My Ryobi is a long shaft purchased new this spring (2005) as a weed eater for $60 or so.

Bill