My neighbor (different engine) had same problem. We just unhooked fuel line from pump & Squirted it full of carb cleaner. Let it sit for an hour, then tapped on the carb bowl with a screwdriver handle. Then applied some air pressure (like 10 psi) into the fuel line for a few seconds to blow the stuff thru. Hooked up the fuel line. It started hard (I think due to carb cleaner/crud) but overflow issue was solved & it ran good once warmed up.