It's those Japanese plugs in old American Iron
Some folks believe AC and Phord brand (Autolite?) work best w/out fouling. Sounds like a tune-up is in order, compression check. Go to
www.yesterdaystractors.com and ask on boards there. These engines were used in lots of tractors and someone more familier with them there maybe. Maybe rings froze from not running much and little or no compression on that cylinder?
