Hi,

Yeah, you're down on power I would say. My Homelite 30cc is souped up, but it will turn an APC 16 x 8 at 9400+ rpms. I've never run an 18 x 8 on it, but it should theoretically turn one over 8000 rpms. You are definitely way down on power with only 6200 rpms.

The very first thing to do is check the condition of the engine. Any more, when I grab an engine out of my big box of used engines to convert for an airplane, the first thing I do is just go ahead and order a Frank Bowman ring for it. Even if the original ring is in good condition, which is rare, the Bowman ring is good for a power boost.

Next, are you running a free flowing muffler and larger carb? Do a search here for Homelite post done by me (and others), and there is a ton of info on hopping up these engines. As Tym1meo said, stuffing the crankcase is one hop up item to do, but all the hop ups in the world won't help a tired engine, so start with a check of the rings, bearings, and seals first.

Good luck,
AV8TOR