Something completely non-military

[Col Tigwell]

If you mow on any sort of incline, the B&S is not a good engine.

At 500 hours mine put a rod through the block, and it is caused by the spalsh feed just not being good enough on inclines.

Your stating problem may be caused by the engine flywheel keyway. What happens if the engine encounters any nasteys, the key itself is design to bend, so the engine timing is out, as the key allows the flywheel to move. Not a bad idea, and I suspect that could be the problem.

Also these engines should not be run on multi grade oils, You can buy straight 30 grade oil, from B&S.

I doubt if there is much wrong with the engine, as you appear to have good compression.

Flywheel off, is where I would start, bet you can buy the special key straight off the shelf. Do not use a normal one, as your protection will be gone.

Regards

Col