Quote Originally Posted by ghosthunter View Post
if you ran on LPG on stock ignition timing, it would be like running on gasoline with your timing retarded which results in less power and lower engine efficiency. In theory, you should have a percentage gain in fuel economy.

The reason why you need to advance your timing is because the flame front of LPG is slower than gasoline. So LPG needs to be ignited earlier than gasoline.
What's your car and how many degrees did you advance it? How many percent increase better consumption did you get after?