Small Engine Troubleshooting Problems? Ask a Mechanic Now.
What is mower doing? Is it firing on both cyliders? Run a cylinder balance test. Loosen the spark plug wires, and with engine idling, remove one wire at a time. Engine should continue to run. If engine dies when one wire is removed, the opposite cylinder is not firing. The pto switch should not affect engine running, other than the extra load on the engine.
You say plugs are fouling? Black carbon deposits? Too little air, too much fuel. Is the choke plate in the carburetor fully opening?
that is anti-backfire solenoid that closes the main jet when key is turned off. It opens as soon as the key is turned on and stays open till key is turned off, then it closes the main jet to keep engine from backfiring when hot. Some people call it a fuel shutoff, but that is not its purpose.
With engine off, can you spin the pto clutch? It should not lock, until the key is on and the pto switch is pulled.
Yes, carburetor problem, float leaking, or jets in carburetor fell out! Here is link showing carb. has two part.s