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Rick, Small Engine Technician
Category: Small Engine
Satisfied Customers: 3844
Experience:  Outdoor Power Equipment technical trainer since 1990, covering eight states.
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I have a McCulloch 300EX lawn tractor with a 22hp &S engine

Customer Question

I have a McCulloch 300EX lawn tractor with a 22hp B&S engine model 91P677 type 0804-B1 code(###) ###-####D
It will start but refuses to keep running now and for some time (since it had a short block exchange done) has been backfiring when you stop the engine. It is reluctant to start on full throttle - prefers to start with just a little throttle - runs for 15-20 secs then stops. Initially it did not want to start at all. The carburettor seems clean and I'm not sure its at all a fuel problem. Could the timing be flawed since they changed the block? Apart from the backfire it was starting and running fine until last weekend. Stopped to have a cuppa and then it would not start.
Bob B.
Submitted: 2 years ago.
Category: Small Engine
Expert:  Curtis B. replied 2 years ago.
31P677? single cylinder Briggs engine. I the carburetor is an electric solenoid, it serves as anti-backfire solenoid. It plugs the main jet when it is relaxed. Sounds like it is not working correctly. It requires 12 volts as soon as the key is turned on and has to stay open for engine to continue to run. Do you have 12 volts to it as soon as key is on? Does it retract fully when it retracts? Should click open as soon as key is turned. It can cause hard start, kill engine if it relaxes, and cause backfiring when key is shutoff!