FYI - There is a repair manual called Small Air-Cooled Engines service manual published by Intertec. It's loaded with information on small air-cooled engines, including factory specs, how to adjust Walbro carbs, parts diagrams, trouble shooting, etc. There is a 1990-2000 edition. Didn't look like Ryobi was one of the manufactures it covers, but it does cover quite a few.

Jeff