Riding lawn mower blows exhaust thru carb after start. Decompression mechanism is not disengaging. Any ideas why?

I have a riding lawn mower that hit a brick.  It's a briggs 17.5 engine, now it blows exhaust through the carb after start, the decompression mechanism is not disengaging.  I disassembled the engine and deactivated the decompression mechanism and the engine runs normal but needs a jump start from my truck battery.  It is disassembled again, can't find anything wrong.  Any ideas?


I had a similar trouble when I hit a rock it was a bent key.

Have you checked all the keys and made sure they are strait fly wheel the gears on the crank shaft and cam shaft.

When you reassembled the motor did you double check the crank shaft to cam shaft alignment.

There should be a marker between the teeth that look like an arrow or a dot that you line up.

Joe