Small Engine Troubleshooting Problems? Ask a Mechanic Now.
The Mower has two belts for the deck, one from the engine to the deck, the other is the deck belt. Is the belt from engine turning? See the belts in link above!
So are the blades turning now? If the belt is turning, the blades should be turning.?? Unless the drive pulley is loose on its shaft and the woodruff key is sheared???
I would not rule it out, but a sheared key could affect the speed of the belt, if the pulley is slipping on the shaft. it would have to be the center . double pulley.
?? So your saying engine speed was down, not the blades slowing? That would make sense!