Today I installed Petronix ignition and "Flamethrower " coil on my recently purchased 620T. Some of you may have seen my post last week where I whined about my poor performance at a pull. I've never been very confident about ignition issues, so I was elated when I followed the instructions and the tractor actually started afterward. It ran rough and backfired a time or two, which I attributed to needing a timing adjustment. About this time, a friend who is much more knowledgable about JD's showed up and said, "it's only running on one cylinder". To prove his point, he took a pair of pliers and pulled the plug wire off the R hand plug, and nothing changed about how it ran. I had already planned to change plugs and wires, which we did, to no avail. I knew that plugs sometimes don't perform well under compression, so we removed the plug, reattached the wire, and ran the tractor as my friend grounded the plug against the frame, and saw no fire onthe plug. With the plug out, the tractor seemed to produce significant compression out the plug hole, indicating the valves seemed to be functioning. Keep in mind that the tractor has performed and sounded like it does now since I bought it a month ago, so this is not related to the new electronic ignition I installed today. I didn't have time to buy a new distributor cap today, but checked the old one with a meter and it showed conductivity to both posts. Any suggestions?