Small Engines (Lawn Mowers, etc.): Loud knock after general tune-up, discharge chute, eager 1

Question
Mower is a Craftsmen 6.75hp Eager-1 22"cut, i performed a general tune with parts from sears, Oil, Spark plug, air filter, sprayed carb with carb cleaner, tightened all bolts, lubed all linkage and cables, and a new blade. when i gave it a start a load knock came from the engine. it vibrated a little heavier than before, but that destinctive loud knock. It seems like something hits on every stroke of the piston. Could it be wrong plug, although it appears to be the same size? Please Help? Thank you for your time.
Fredo

Answer
Hey Fredo. Toughen up. The knock you are hearing is the blade being loose. I gaurantee it.

Pull your sack up and tighten that blade.. Wedge a block of wood between the tip of the blade and the discharge chute to hold the blade. Now TIGHTEN the blade.  Remember how hard it was to get off? That's how tight it needs to be on. Freakin Tight!!!!