I had a 4020 LP and overhauled it. In reading the manual it said to put the flywheel at the TDC position and do this and do that.
I had every JD jock in the county out here trying to figure out why it just wouldn't work to no avail.
One day I decided to go back to the manual and read through the setup again and WALA. A one liner that said: "When you have finished with the preceding procedures, SET THE TIMING TO 25 DEGR. BTDC...........................DUHHHHHHHHH!!!!!
That was that.
My personal experience with that fuel was very disappointing. The tractor was very picky and was hard to start after running. The fuel ran hot and sitting in the open station, as compared to a comparable diesel was extremely uncomfortable in the summer.
I had a nurse tank on wheels that I towed around to service it. In the summer, when working the tractor, unlike diesels I had later, it had to be refueled at least twice a day and to refuel a propane tractor in 100 degree heat with the engine hot was more than I could stomach.
I fired it.