Okay it's not a car, it's in a generator, but I couldn't find anywhere better to ask.
I've got an GX620 Honda V-TWIN it runs fine on petrol but won't run on lpg, it's meant to be dual fuel. If I block half the air intake it will run, but doesn't have enough power to cope with any load. Runs fine without blocking air inlet on petrol, and has full power etc.
Anybody any thoughts?