Yeah, I'm not sure about the size. If I tear it down, I'll measure the bore and stroke. I have two of the sears/poulan engines and one of them is a 22cc, it has a label on the trimmer head. I looked at the parts diagrams for both engines and they share the same case, but the crank, piston/rod, and cylinder are a different part number. It is from a 'brushcutter' so it probably is a bigger engine.

I got the thing mounted on the test stand last night and tried to fire it up. I discovered that my 12v starter that I use for my small glow engines isn't up to the task. Then I tried my 12v cordless drill and it isn't really up to it either. It spins it, but not fast enough. I put an AC 3/8" drill on it and that does the trick. I couldn't get the engine to run for more than a few seconds though. It was either getting too much air or not enough fuel. The spark looks good. I took the carb off and stopped by a repair shop for a carb kit for it. While examining the carb at the repair shop, I found that a piece of the old fuel line was stuck in the fuel nipple causing about 90% blockage. When I get home tonight I'll clean out the blockage and try it again. If that doesn't do it, I'll rebuild the carb and try again. I'll get some pics of it on the stand tonight (hopefully running).