No accelaration in my Range Rover classic

hello,
i have a 1985 classic range rover with an lpg conversion.
Earlier this week after starting and driving all fine, i stopped. On starting up again, it fired and started, but there was a loud 'pop' noise. On pulling away, it drives and goes through the gears, but will not go above 15mph!!! It idles fine but will only rev to about 2000???
Any ideas???? It sounded like maybe something popped off or loose???

Please help!!!!

Many THanks

Nick

its popped back through the inlet and wrecked the air flow meter, have a look and you'll more than likely find that the air box is in bits!