If you are loosing spark on one cylinder once its hot, it's a bad CDI box, which is a very common problem with that model year. Actually - the guy I bought my first JD sled from (76 - 440) thought it was the CDI also. He eventually replaced the stator = since he could not return the CDI he gave it ...

John Deer made a set of slides/cassette courses on this and other subjects. I have the slides and cassette and had them put on the internet a couple of years back. I cannot remember the site but any tuning or alignment for racing or otherwise is on this set of slides. The site had manuals for most o...