Should be a Suzuki engine. Could it be possible that the blade hub key is damaged and partially sheard the flywheel key?

Rolm: Your experienced within these issue Dude ! Did you hit anything last fall ? As tom has questioned either your blade is loose or your shear pin assembly is damaged or possible crankshaft damage . Remove the plug wire turn over the mower carb side up and check the blade and fasteners. Next pull the mower and observe the blades rotation. If all appears ok then check the shear pin , it may be partially damaged (split) or twisted causing improper timing and starting .
One would assume that PM has been done previously on Fuel and Air filter is clean along with fresh fuel ?

It�s Fixed 1-Pull Start and it runs like a dream. I refused to give-up on such a jewel of an engine mind you this is a 1988 Toro with a 5-hp Suzuki engine.
I found it odd that it would take 10 to 15 pulls to start and there would be a clanking sound and then it would run smooth. I bet there would have been zero power I did not have grass to test it on a bit early for grass in Toronto.
Two things that threw me were 1) the blade had a few small nicks no big deal and 2) the pull cord did not kick back. If the blade was damaged and if the engine kicked back my 1st thing I would have looked at would have been the flywheel key and that was the problem. Once I replaced the flywheel key and it starts in 1-pull and it runs like new.
Thinking back the clanking sound was the knocking of the engine due to the timing been off.