Any Ideas what's wrong with this mower?

I am learning small engine repair, and right now I'm working on a mower. It came to me unable to keep running, seemed to flood and die. I did all the obvious stuff, replaced the spark plug and air filter because both were filthy, changed the oil which was basically sludge. The mower is running better, but after using it for about 20 minutes it dies. It also gets pretty hot before stopping. The cooling fins are clean, but the housing on one side is lower because of a wheel that's jammed in the wrong position, I need to figure out how to unjam it. Also the blade is very dull, has almost no cutting surface left. Could the dull blade be causing the engine to work harder and to overheat, and is it possible that the low rear housing on one side causing the blade to drag the ground and kill the engine? I don't feel or hear the blade dragging the ground, but it does seem to me that a dull blade would make the engine work harder.