Thread: Off topic: B&S 12HP engine fault

I have a problem with my ride on, it has a 12HP briggs and stratton engine. Fitted a new battery, new oil and a fresh tank of petrol this morning(it had been idle for some months).

Ran beautifully for 20 minutes, then it lost power. At idle it'll runaway and revs its nuts off even on the lowest throttle (like a runaway Tdi) and it hasn't any power. It backfires when shut down.

I was thinking maybe a burnt/cracked valve?

Any wisdom?

sounds familiar
mine has them symptons, heres what i did but didnt cure it, new head gasket, spark plug, new float needle, stripped carb about a dozen times, woodruff key was out of alignment on the flywheel ( fixed that ) check spark output.. ok , check valves, cleaned fuel tank, replaced fuel lines etc, replaced air filter, replaced exhaust gasket, so on so on, never did find out what was wrong , so i got another mower and it started to play up with these kind of symptons and i took the engine out and the sump bolts had come out , i fixed that and it fine now. so maybe thats whats wrong with the old one cos i found bolts on the decking that look like sump bolts.so if needed i will sell you my old mower dirt cheap for spares .
hope this helps some

taslev