Small Engines (Lawn Mowers, etc.): LAWN MOWER, precise tolerances, spark plug wire

Question
i HAVE A CRAFTSMAN 7.0 HP 21" HI-TUNNEL MULCHER, FRONT GEAR DRIVE.
MODEL #: 917-378642; SERIAL #: 031703M002722.
IT'S BEEN RUNNING FINE UNTIL TODAY. I CHECKED THE OIL AND IT IS AT THE CORRECT LEVEL; GAS IN TANK. I MOWED PART OF MY LAWN WITH NO PROBLEM; THEN IT SUDDENLY STOPPED. IT WAS DIFFICULT TO RE-START IT, BUT EVENTUALLY IT DID. BLACK SMOKE CAME OUT OF THE ENGINE FOR A SHORT BURST, THEN CONTINUED TO RUN. I PLACED IT IN GEAR AND STARTED DOING THE LAWN, BUT WITHIN A FEW MINUTES, THE ENGINE STOPPED. I DIDN'T WANT TO RE-START IT AGAIN, FOR FEAR THAT I MAY HAVE DAMAGED THE ENGINE SOMEHOW. I HAVE HAD THE MACHINE FOR ABOUT 2 YEARS AND NEVER CHANGED THE OIL. THE BLADE COULD USE A GOOD SHARPENING AS WELL.

Answer
BOB

well Bob you just answered your own question,sounds like you have a carburetor problem.Some of your symptoms could be ignition related. Check your spark plug wire connector for a tight fit of the metal connection to the top of the plug, not just that the boot is holding the wire in place.Try loosening the gas cap. The cap vent may be plugged

If you don't do anything else to prolong the life and happiness of your small engines (and your automobile, for that matter) it should be an oil change at the recommended interval. Oil loses its lubrication and cooling effectiveness with use and this will gradually take its toll on your precision engine parts. Even a simple lawn mower engine is machined to very precise tolerances and any contamination will increase wear. Ultimately, its performance - starting and running - will suffer and its life will be shortened.