20 Mpg!!!!!

[unkleG'sif]

Happy new year guys and gals

Just a quick question before i dash off with work..... something that has been troubling me for a little while

Ever since I had a new engine fitted (blew exhaust valve and a good head came with complete engine) to my LPT, and had it FPT converted with the system from the car the engine came from..... ive never had an average MPG over 20.... which is quite bad when I drive 20 miles to work everyday (and back) ..... and work for a charity - so the old payslip is a tad thinner than my actual worth
Other people seem to have reported 25-30mpg here

Im just trying to bounce some ideas around here, but for some reason I think that the problem could be with the Lambda Sensor. I base this crude assumption purely on previous posts regarding AMM adjustment, and this being irrelevant on cars with Cats and O2 sensors.

Basically the car is in good order, well serviced, and have checked the usual things (tire pressures, brakes rubbing etc)

Does anyone have any more advanced tips that I would not otherwise have thought of?

Gotta go now, but ANY advice would be HUGELY welcomed as I cannot afford my petrol bill at the moment
Adios
G