MY 1995 Ford EF Fairmont, 4.0-litre six, which runs on dual fuel, keeps backfiring on start-up particularly after being idle for a few days. I know I should start it on petrol then change to gas after a few seconds or when the throttle is depressed, but I have no way of knowing if this is so. It always coughs on the first key turn and starts every time on the second key turn and stalls if the throttle is touched before starting.
YOU don't say if your car has a factory LPG system or an aftermarket one, but I will make the assumption that it was a Vialle system fitted by Tickford for Ford. The Australian Liquid Petroleum Gas Association says its important for good running that the ignition system be well maintained because LP requires a stronger spark than petrol to fire. Make sure the ignition system, plugs, leads and ignition packs are serviced, and the LPG converter is properly drained regularly. The Vialle system was imported by Boral Gas, so if you still have problems, ALPA recommend contacting Boral for advice.