3.5V8 LPG cutting out

Hi there guys can anyone help, just been doing a few short trips 2-3miles to help people collect timber and travelling back GAS/LPG cut out but noticed that when i accelerate it flows again. On the Gas/Petrol switch when on petrol red light on all ok, when on gas amber light comes on at first all ok when i'm revving, then as i adle the amber light goes out turning of the supply, but if i'm quick enough on the revs it comes back on. She runs fine on petrol, has anyone else come across this?

Engine bay seems to be getting very hot

many many thanks in advance
fairly novice to engines

regards Scrumpy....