my lpg car gives a poping sound when i start , like back fire?

Question

what does this mean and what might be the reason for this , and please give me address of any good lpg mechanic in melbourne , australia ,Thank you !

Answer 1

Billy—
There is a good probability that the fuel control for the LPG isn't sealing the fuel completely during the OFF condition. This will allow gaseous fuel to enter the plenum area and "flood" the engine.
When the engine begins to revolve and a spark is introduced, the fuel in the plenum ignites and you hear the POP.
Where to go? Can't tell you Mate. Never been down under. Like to come some day, but not sure that will ever happen now.

G'Day, Mate

Answer 2

I'm familiar with LPG forklifts, but i hope to still help you with your car.

The most obvious would be a gas shutoff valve that is worn, or not closing all the way allowing the gas to collect in the intake system and since LPG is heavier than air, it makes it's way down to the exhaust system while parked.
Then, when you go to start it, the accumulated vapors ignite.