Small Engines (Lawn Mowers, etc.): Poulan 42 Mower with 18 hp B&S No Start, fly wheel, shear pin

Question
I have a 5 year old Poulan 42" Mower with 18 hp B&S OHV engine. It has always backfired on shutoff but tonight my son was mowing, shut the mower off, then when he went to restart it wouldn't. It has spark but doesn't seem like it has any compression. It's backfiring worse than ever. Overall, I've had pretty bad luck with this thing. Late last year reverse went in the 6 spd transaxle.

Answer
Ray
It may be out of time check the flywheel shear pin to see if it is lined up with the notch. You will need to remove the top housing and then use a impact to remove the bolt on the flywheel. If you look at it and it is not lined up then you need to pull the fly wheel and install a new key way so it all lines up.