I replaced the oil pan gasket and reinstalled the engine on my JD 345 (18 hp ). It started for about 5 seconds then stalled . Now it is back firing through the carb and will not start. I would appreciate any help

Hi,
Sounds like a sheared flywheel key. I do not remember if the older 18 HP had the control module used on the 20 HP. If it does, it is a canister-shaped piece with three wires coming out of it fastened at the left rear corner of the engine by a cable tie.
Peace,
Clarke

Found the problem . Broken camshaft gear , its made of plastic. Had to replace the whole cam and tappets though. The new cam has a metal gear.

Hi,
Thought all those would have failed by now!
Peace,
Clarke