I recently rebuilt a briggs 12.5 hp I/C motor and I can't get it to start. It will rotate but when it tries to start it backfires. I had the whole engine unassembled I'm just wondering what could have went wrong?

Did you line up the timing marks on the cam and crankshaft closest together, not one at top and one at bottom. Always close together. Then if you timed it correctly there. I would mainly lean toward a sheared flywheel key.

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Originally Posted by MOWERMAN2468

did you line up the timing marks on the cam and crankshaft closest together, not one at top and one at bottom. always close together. then if you timed it correctly there. i would mainly lean toward a sheared flywheel key.

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Sheared flywheel key? Do you mean a missing tooth on the flywheel or the key is actually sheared. The key is fine but I am missing a tooth. Also my spark plug was wet like it wasn't firing.

See the reply to the pm you sent.