I have a very old John Deere rider lawn mower. It seems to run quite well, but after an hour or so, it starts cutting out and then quits. Do you think this is a fuel problem, electrical problem... or is it possible the motor is overheating and quitting?

The reason I am concerned about overheating is because the hood has NO openings for the heat to vent away from the motor. This being an older mower the hood has no holes. I notice the new mowers do.

Another thing that puzzles me... the fuel line coming from the tank connects to a small rectangular metal box. Then out of the box are 2 fuel lines. One obviously going to the carburetor bowl... and the other runs into the engine. Can you explain what this box is and what is its purpose.

Thanks,
dbteeitup

The "rectangular thing" is probably a charcoal canister to keep fuel vapours from going into the atmosphere.

"Electrical problem" - Check for spark when it dies
Fuel problem/square thing - possibly. Check for a wet plug after trying to start it when it dies. Use a little carb cleaner in the air cleaner to try to start engine. What happens?
Sputters?

A little piece of dirt in the fuel system from a rusted gas tank can cause these sorts of problems.

What happens when you keep the tank no more than 1/2 full? Does it die?