I think the black tank is a heavy duty home model, my black tank model was 8430 not 8431, I have had both, the red tank and wheels had the guard, the black tank and white wheels did not, the red one had an all metal carb, the black one is plastic and metal. Both use the F series engine. So other than the outer appearance, with a little maintenance both will last forever. Have a good one. GeoHi , just wondering if these black tank models are true commercial mowers or the heavy duty home owners version ? Also did they come with a metal gaurd ?