Hi. My roommate hit a stump with my mower, and I replaced the blade, and flywheel key (it was sheared). Now, my mower runs very rough, blows black smoke, and stalls under heavy load. It also now uses twice as much fuel as before. I've also replaced the spark plug. The engine is a Briggs and Stratton 6.75 HP 190cc engine. Model number 125K02 0281. I've only had the mower about 2-3 years. Any idea what is wrong and how to fix it? Thanks in advance.

For starter, I suspect you have a bent crank. I don't know if that would cause the other problems, but you would definitely feel some vibration in the handle when running.

Check your air filter for oil contamination. Chances are when the mower was tipped up for inspection and or blade replacement oil made it's way out of the breather and into the air filter box. Try running it without the air filter element in place and see if it clears up and runs smooth. If it does, then purchase a new air filter element and install it.

Don't use your mower without the air filter element installed as you can ingest a considerable amount of dirt and debris in just one mowing without one.

Good Luck... :thumbsup:

The air filter was exactly what it was. I'm very relieved! When you said air filter, I was trying to think how that would produce the black smoke, but then it occured to me that if the carb is getting less air, but the same amount of fuel, it will automatically run too rich. This also explains why it was using twice as much fuel. I took the filter off, primed it, and it cranked right up and purred like a kitten. Thanks so much.

Ok, after a bit of procrastination, I got a new air filter, mower ran fine for a bit, then I hit ANOTHER obstacle, this time a small but solid piece of wood. After that, it would not start again. I checked the flywheel to make sure the flywheel key hadn't sheared again, and it didn't. The key is fine. I don't know what else it could be. Any suggestions?

I would try a new spark plug, if it was running rich prior to this then there may be enough carbon on the plug to be causing a problem. If the key is good then whatever is causing the mower not to start, is most likely not related to the wood you hit with the mower.

I put a brand new spark plug in it since all this, and before running it this time. I did not, however gap it. I wonder why it cranked right up and ran great then refused to after hitting the obstacle?

Well you should check for spark just to make sure about that, then make sure it's getting fuel, try priming it to see if it will start and run out the prime. Perhaps there is something plugging up the jet in the carburetor.

Um, although this reply is several months late, my mower did eventually start up and run fine. Don't know what caused it not to start the second time, but I gave it a while and decided to try it again, and it's been working fine since. Thanks for all the help.

Great !! Glad to hear it's going well for you.