Well, I finally got back to this tiller last night. I pulled the head off and sure enough the exhaust valve was stuck open. Sprayed it with some WD40 and spun the engine to cycle it for a little while and got it freed up so that it is now cycling on its own when I spin the engine. The head gasket actually looks really good too so I think I'm going to be able to re-use it (at least for now). When I put the head back on, I know there is a certain torque to set the bolts to, and I think there's a specific order to torque them in. Does anyone know what the order and torque are?
Thanks again for all of the help so far!