Tractor Repair: 1960 Ferguson TO-35 Fuel problem, dirty air, burning oil

Question
My tractor had about 20 hours on it from the last tune up, and it started missing and cutting out with a cough. When I got it home, I pulled the plugs out and they were covered in black yuck. I cleaned them up and got another set of plugs and they ran fine for about 6 hours and then the same thing. I know it's not an oil problem, because it doesn't smoke all the time. Could I be getting bad gas, or is it something in the carb? Maybe the spark isn't enough?

Answer
Hello,


  Was the black stuff on the plugs wet or dry?  If it was dry like black soot, then it is getting too much gas.  That could be a carburetor issue or dirty air cleaner.  Also weak spark or the wrong spark plugs.  If it is wet sludge on the plugs, that means the engine is burning oil.  You said it doesn't smoke all the time.  Does that mean it smokes sometimes?  It shouldn't smoke at all.