Morris Minor Owners Club

forgive for being a bit naive' but how does the petrol mixture help with M.P.G. If you run rich does it mean that you use more petrol or is it vice-versa I know the mixture has to be set at a certain level to maintain a good tickover etc. but I was wondering about the M.P,G. as my car seems to be using a bit of fuel, but it sounds sweet enough.
sid

Yes, richer mixture = more petrol being drawn into the engine.

You only want the optimum amount of petrol to go into the engine or it will not burn properly and will come out of the exhaust as black smoke which smells terrible and damages the environment and your purse/wallet.

The optimum air/petrol mix is approx 14 parts air to 1 part petrol. This gives the most efficient running mixture and provided the carb is in good condition with the correct needle and the ignition timing is correct, then adjustment of the mixture screw on the carb to obtain the fastest/smoothest tickover will set the mixture at near enough the correct ratio.

Simple check - after a good hard run (ie no stop-start through traffic) , whip the plugs out for inspection. Black = too rich, white = too weak, beige/tan = just right!