My 20015 riding mower has this surging thing going on, it started doing it last summer and and wont come out of it. I tried Sea Foam and few other cocktail mixtures, still acts up and think it's getting worse cause it barely started couple weeks ago and have to run it with choke on a little, guess I'm gonna have to take carb apart and see if I can make it run worse. This thing is only 5 years old, I have a 30 year old wood splitter that starts every fall and runs still runs like new.
Sears riding mower P-1 - YouTube
Sears riding mower P-1 - YouTube