Oil keeps fouling the spark plug on my ancient 20" Murray lawn mower with a 3.0 hp Briggs and Stratton engine. What could the problem be? Thanks.

Oil breather, rings, valves.

You can try to find a 'hotter' plug to try to prevent the fouling - usually just means a longer tip and bigger gap but I could be disremembering it.

Again, any competent yard equipment supply house would be able to give you the info - they will probably want to rebuild it but should give you the plug number for the hotter plug w/o a big hassle.

Tell 'em it's your father-in-laws mower and you want to help but not invest or something if you must tell them something...

To rate if you found it helpful...

You can try to find a 'hotter' plug to try to prevent the fouling - usually just means a longer tip and bigger gap but I could be disremembering it.

Again, any competent yard equipment supply house would be able to give you the info - they will prolly want to rebuild it but should give you the plug number for the hotter plug w/o a big hassle.

Tell 'em it's your father-in-laws mower and you want to help but not invest or something if you must tell them something...

to rate if you found it helpful...
Why lie about who's mower it is. Rebuilding a 3hp briggs is more expensive than the price of a WHOLE new pushmower at wal mart by the time you count the parts and labor. Come on now, be honest.

Thanks for the advice. It's definitely worth fixing - I'll try the hotter plug. A brand new lawn mower is not in the cards. Lately, I've just been buying a new plug when I want to cut the grass - which hasn't been that often. I'm in an area where we're having a drought, and the grass hasn't been growing. Next year, no doubt there're be lots of rain and I'll have to find a permanent solution. Again, thanks.

No problem. Just don't let some shop talk you into a complete rebuild, cause you will have too much tied up in the machine vs. purchasing a new one with a larger hp engine and not to mention a warranty. Use caution though, the new mtd's with mtd engine is not my cup of tea so to speak.

About this time every year, changes come about that will fill your heart with gladness, yea, verily, I say unto Thee, divorces smite marriages and garages vomit forth God's Goodness of power tools and lawn machinery. The Devils' spawn of subprime mortgage brokers smite the households of those new to mortgages and payments that are like boils on the behinds of the saintly and thus do also garages vomit forth God's plethora of power tools and lawn machinery.
So take thyself to the Land of Garage Sales, Estate Sales and Greensheets to find and feast upon the treasures of the land, a bit used but much usable.
And beware the dreaded MTD, the once praised and now much maligned.

I bent my brain so bend yore pen and rate this answer.

mtd = mostly total disasters.
ha ha, just a little humor.