Missfiring, occasional backfireing & hesitation on LPG

[dom14]

Sounding good (plugs, leads, and then mixture).

Your impco gear maybe old build but when set good you can leave it pretty well alone.

IMO set it up for your preferred fuel and for sure keep other fuel bits in your tool box if you get stuck. If you run LPG majority of time, go that way, but is always good to cold start up on petrol then switch over to gas and is beneficial to occasionally run say 20kms on petrol every couple of months (your cal) just to keep that side of your sys all in a serviceable condition. LPG is a dry fuel compared to petrol. I guess you do understand this...

Yeah, mate, but it is a 'contentious' subject.
Starting on petrol is particularly a good idea in colder climate as the LPG converter need coolant warmth to function properly(I reckon some of them are built that way, probably not all of them).
I believe(which means my logic may be flawed ) starting on LPG has it's own advantages when the engine's cold 'cos petrol has solvent effect(colloquially called "wash effect") and when cold start an engine on petrol the mixture is super rich and that can cause extra friction on the piston rings, and cause extra wear until the mixture is stoichiometric. Since the LPG is not a good solvent 'cos it is a gas in normal temperature it probably won't have that solvent effect. It is my belief a properly setup LPG system can extend engine life more than a petrol engine.

And I agree with you after having this dual fuel RB30 for over six years. Dual fuel may be a tricky idea, even with hightech units like dual curve units to adjust the difference between two fuel's combustion style. I prefer to tune it for LPG, but then again it's using a petrol carby to control the throttle and idling(partly).

LPG causing extra valve recession is mostly due not tuning/timing it properly, I think.