Tecumseh 9hp engine trouble

I've got a Craftsman Snowblower (536.886261) with a 9hp Tecumseh engine (143.029003) thats having some issues. Pull start jerks back and is almost impossible to turn over without the spark plug out. Broke the teeth off the starter as well. I've ground the valves and everything is fine there and I didnt notice anything unnatural when the flywheel was off. Snowblower has only been used a few times and sat in the garage the rest of its life. Just hoping for a second opinion to see if I overlooked anything obvious. I'll probably check the compression release next and post an update soon.

Jerking back when starting is usually caused by a sheared flywheel key. If you had the flywheel off and didn’t torque it properly, it probably sheared the first time you tried to start it. Second, you engine is a model HMSK90-156536E, which leads me to ask, did you set the valve clearances after grinding and lapping the valves? Personally I doubt that there is anything wrong with the compression release, unless you opened the engine and had the cam out. Do you have the correct plug, should be a Champion J19LM or equivalent. If you have a long reach plug it may be hitting the piston. This manual might help you out. https://mymowerparts.com/pdf/Tecums...P-4-CYCLE-L-HEAD-FLAT-HEAD-ENGINES-692509.pdf