It only has 30# of compression after another look.

Heh heh, I spent all sorts of time tinkering with a 5hp Tec on my Ariens. Finally it wouldnt start, ignition failure far as I could tell. I re-engined with a 6 hp re-man with electric start that I snagged from an old Bolens

Sometimes we overlook the obvious, easy to do.

It's making sense to me now. I get it started and the high rpm overcomes the 30# compression until it meets a load.

So, I'm looking at valves that don't close fully, or leaking head gasket. The motor doesn't seem too old or even abused.

Turns out it was an exhaust valve with no lash. Relieved the end and now has 90# compression.