self propelling system got really slow

[ccdk]

I have a 10 year old Partner p53-875dwa with Briggs & Stratton engine.
Yesterday I hit one of the legs of trampoline in the garden by mistake and after that the self propelling system got really slow. It is still turning, will but really slow.
As an experiment, I started walking while the mower is on, then pulled the handle to activate the self propelling system, it feels like the system is putting a break as it is even slower than my walking speed.
Edit: I checked the belt and it looked fine. Any idea what might be wrong, can gear box might be the issue?

 

[Fish]

Likely the belt has jumped off. Don't run it long.

 

[ccdk]

Thanks for the answer. I checked the belt before and it looked fine, it is attached and turning as as it should.

 

[Fish]

I mean jumped off where it rides on the engine pulley. If it jumped off, and is riding above the pulley on the shaft, things would still work, but much slower. And the belt won't last long either. Those belt covers cover things pretty close to keep debris out, so it is hard to look in there.

 

[ccdk]

Thanks for clarification, I will check the engine pulley if it is riding above.