3.9 Lpg Rangerover Problem With Airbox?

Hi i have a 1990 3.9 Vogue Se fitted with a LPG Conversion, This is my first L/rover and im having problems with the airbox. when the car is running on petrol its fine, but when on LPG problems start. when its idleing its fine but after selecting drive and putting some power down to set off theres a massive bang under the bonnet and the airbox is all in bits and smoke coming out of the Plenum chamber on the top of the engine, ive changed the airfilter but its still the same,

Anyhelp with solving this would be great

Cheers

ohhhhhh dear. this sounds like a single point system that is miss behaving. some pics would be useful to determine that the gas anulas is in the right place and the system layout. it may be just a poor fit as it should run well. backfire is also a symtom of dead ignition leads and/or plugs. ignition timeing is also key factor. some more information would be useful, LPG manufacturer name and type. you say the airbox was blown apart, what about the vain meter? does it still move freely?

Hi
This is a typical problem it is lean on fual, you can purchase a backfire valve fom Stephen at Autogas 2000 01845 523213