Since Yale has multiple LP systems on trucks depending on the year, a serial number would help. Each system came with new items to check. Your local dealer should be able to help. Send your serial number. This could be a failing diaphragm, high LP pressure, weak spark. Check your cap if it has it. Plug wires and plugs. Spark plugs at known to wear faster on LP systems due to higher heat.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.