You won't find a lot of people here running LPG.
Here is an interesting article:
Originally Posted by Departing90
The EFI system on the 3.5 Rover is basic with a ECU that controls the fuel / air mixture via again basic sensors. Timing is set and and can be slightly adjusted by tye distributor as in distributor rotor points to cylinder #1 and timing mark on harmonic balancer lines up for TDC. If the engine was running well prior to tye installation of the LPG unit I would strongly suspect the LPG unit or tye installation. Might be better if you posted on a UK forum where people have much more experience with the particular LPG system youve installed or try calling tech support of tye manufacturer.
In order to get the correct timing advance, the distributor would have to be fitted with different or modified weights and springs to alter the advance curve.