Poor mpg could be blocked filters. You can tell because there will be a runny white substance inside. They should be changed every service (annually or 200 hrs).

Or the vacuum needs replacing.

I bet yours hasn't had a service in a while. Get it serviced and see the difference.

Hey TB10 how did you get on with your research?

Not far I'm afraid as other issues have taken over. I will look at this in the New Year.

Kind Regards

I have a 4.2sc lpg converted and get around 180 on tank around 75 litres.

My driving is very mixed and a lot of school runs which really kills the mpg, I'm averaging on the computer which is calibrated for petrol around 15.

Hope this helps.