Why do the spark plugs foul up so fast on my 1956 Ford 860? In the winter plowing snow after 1/2 hour I have to change the plugs since they are 100% black, in the summer I can rake hay 3 or 4 days before they start fouling up. I had the engine overhauled a few years ago and that made no difference, put a new carburetor on that didn't help so my mechanic rebuilt the old one that didn't help either. and we adjusted them the best we could. Still have to pull to choke to start it. I put a !88 degree thermostat in instead of a 180 thinking if it run hotter it would help, it didn't. This is the tractor that would start below zero for 40 years if it would turn over 3 times on an old battery.