I had a 4020 LP and spent a lot of time and money trying to get reliable operation out of it and it just didn't happen. Every day, every hour, different time of day, different engine temp, all were a variance in getting it to light off.
However, in support of your suggestion, I did get CD ign. for mine and it helped a lot.
Oh, and that was the same tractor that I bought that had these little holes down the side of the block with oil oozing out......HA!....another cost of an education........during the overhaul I realized that it was a premature failure caused by the previous mechanic (who-whatever that was) put the wrong color sleeve seal against the fluid to be sealed; had them backwards.
Selling that sucker and buying a diesel was one of the best things I ever did.