Outdoor Power Equipment and Small Engines - mower lost power

i have a self propelled bolens walk behind mower and i cut some tall grass with it and now afterwards it seems to barely have any umph...if i tilt the mower front end up while it is running, it will stop. it also seems to be quieter and just overall weak..but the self propel mechanism still works. what could be the problem?

i tried cleaning the air filter thingy and removed the muffler and ran it and it was still the same. i also checked the throttle cable and it pulls the switch as far as it could go...

thx..

What engine is on it?

http://www.bolens.com/webapp/wcs/stores/servlet/product_10151_15953_91372_35210_-1#
it think it is that one...looks like it and the specs match i think

it's a briggs and stratton,only 2 years old
and it has automatic throttle...

I'd wonder if something jammed into the governor spring area and bent the tab that the spring connects to thereby dropping the top RPM. Have a look and see if bending this tab back into proper position helps. Don't overdo it, as the engine may tend to race out of safe range.

well took it to the repair shop and it was the carburetor and fuel pump thingy. only cost $40 so not too bad. thx guys