P38 V8 performance probs and subsequent fire

Hi Guy, Ive recently bought another P38 V8 with LPG...for 6 months she ran fine, then started having performance probs, she'd drop down to 2000 rpm, and 20 mph...limp home mode , then pick up again and be normal.....now she'll run and rev fine for 100 m but then has back fires and farts.and revs drop and speed goes wayway down.
Took her 4km to a local garage, but owner was useless, driving home the problem got worse, slower and slower, got home, left her on the driveway 1 hour later there was lots of smoke coming out of bonnet and getting worse...l filled up buckets of water, lifted bonnet, and there were flames coming up the bulkhead drivers side, chucked water in, big flash and bang underneath, chucked another bucket in and the fire went out, let her sit for 1 hour. started her up and she ran ok up the drive but revs dropped again. We've tried all sorts of electrical , computer remedies but nothing has changed....have I just had a cat fire and if so what can i do about it?...do i need to replace 1 or both or can i get a length of pipe to fit and ditch the cat...will this afftect my MOT emmisions...any suggestions please...haven't had to call trumpton yet

Blimey!!

First off. Is it running bad on petrol or lpg?
Can you smell lpg under the bonnet?

Backfires and a real fire sounds like you have an lpg leak somewhere!!

Chucking buckets of water

Now it’s out what was actually on fire? You don’t say what year but I have had smoke from the big flat earth lead that dropped near the exhaust manifold and got rather hot.

You don’t say if you were driving on lpg or petrol.

Cats are way down so forget them.

J

oh dear

Why restart it after a fire?

Thor or Gems?