As you know, Ty, I personally favour the "comparison carburetor" process. I take it that in your extensive supply of light engines you would have another Ryobi engine the same as this one. Why not test one of them to verify it is running properly, then try a carburetor swap to the problem one and see how it behaves? It would be irritating to go through all this and then find it is something dumb like a crankcase leak.
