I bought my Mk1 factory LPG last November (I thought it was marketed as the "Dual Fuel"?!) and negotiated a deal based on it running rough as nails. Read up that LPG cars liked smaller plug gaps also so pulled the plugs and checked the gaps. Standard 1.3mm "out of the box" measurements. Haynes said 0.9mm IIRC. I reduced them to 0.8mm. Runs sweet as on petrol, fine on gas on the motorway but terrible around town.
In an effort to get to the bottom of the issue, I had the MOT tester test the emissions on gas to find the CO was really low and the HC / NOx (can't remember which one without the test sheet in front of me) was really high.
Trouble is, I've no access to any maintenance data for it and living in Brighton, there seems to be a void of 'Gas' installers/servicing within a 50+ mile radius! 🙁
Mind you, getting 300+ miles to a £23 tank full, I'm still smiling! 😀