I finally retired a 1976 Jacobsen 21" a few years ago (truly great piece, only replaced head gasket beyond usual motor maintenance), and replaced it with the cheapest Home Depot piece there was with a closed deck (mulch deck & blade). Maybe $150.00. Bought some steel ball-bearing wheels to replace the cheap plastic ones, and it's just fine on the teeny lawn we have (20-30 minutes versus 3-hours plus).
Gave it a hard run one day (late winter); while still hot, tilted the deck and braced it to hold the Tecumseh spark-plug opening in upright position. Gave it a couple of ounces of LC and returned an hour later to pull it through a couple of revolutions. Let sit overnight. Added some more LC to crankcase, fired her off, stood upwind, and and ran for five minutes after complete warmup (Throttle is locked in 3/4 position). Did all other service, added FP-enhanced 87-octane and was very pleased at the improvement in starting and running.
Figured I'd just throw away the mower after 3-5 years versus the time and trouble of maintaining a more expensive machine (mow at least monthly in December/January/February; weekly otherwise and twice weekly April through July); but the LC/FP combo seems to keep it clean enough to extend that considerably. The FP in the gas is the real difference, IMO.