Now maybe I've become a believer. I will dump the old gas, clean the
carbs, change the oil, install new plugs and give it another try.

I've got a short cut cleaner - sea foam. Put in spray bottle and spray in
carb while running. Do it several times. After that put a bunch in the gas
tank with it nearly out of gas. Qucik and dirty - normally works wonders on
my gravely kohler engines. After this, I pressure wash the engine, new plug,
new filter new oil. engine runs like new.

Works on 2 cycle also

Karl