I have a hyster here( d187vo3876t propane powered) that initially ran rough and backfired, now doesnt run at all. It has spark and turns over fine. Propane is pressurizing the intake. After cranking propane can be felt comming out of the pcv valve aswell as the vacuum line that goes to the lockoff valve and the converter valve keeps icing up. Any help would be greatly appreciated. Thanks in advance.