I also have an older tractor which will foul a spark plug every couple of weeks. There are a
couple of old tricks to lengthen the time before you have to change the plugs. One is to pull the plug
wire just a little bit off of the end of the spark plug, this causes the spark to jump this gap you
created and a slightly fouled plug will start working again. There used to be a product for sale
which you placed between spark plug and wire to do the same thing.
One other thing you can try is change to a higher heat range plug if they are available in the size you
need. The numbers have been changed in the past few years but my Ford calls for H-10 plugs, I have
used H-12 plugs with good results. Ask a good auto parts supplier for a little hotter plug.
The truth of the matter however is the rings on your tractor are not sealing like they once did, now
a little oil is added to the combustion chamber as the engine runs evidenced by the smoke you see.
Might be almost time to give your tractor engine a little overhaul.
Randy