My 6.5 b&s ohv self propelled mower starts fine and runs good until the engine heats up. It doesn't die but runs poorly, looses power and puffs black smoke. It has also started using triple the amount of gas. HELP?

Check the flywheel key, it's possible that it may be partially sheared.

If the key is good, then I would replace the magnetron module, I have run across a few of these engines that would loose power and have excessive fuel consumption with a bad magnetron.

Best of Luck....

Thanks for the help. I keep the maintenance up on my mower, oil changes, air filter,and always drain fuel in the off season but I had no idea where to start with this problem. I will get to it and let you know how it goes.

Thanks again