10 MPG on LPG

After filling up the tanks a few times I am only getting 10 MPG on gas. It is an AEB single point injection with a Romaro super vapouriser. I will be changing the plugs, leads, dizzy cap and rotor arm next week. What I need to know is can I set the gas flow up using the large valve in line from the vaporiser to the inlet manifold ? I have read a few things that say get the wife to hold the revs at 3000 and screw the valve in until the revs drop then screw the valve out half a turn, is this correct ? Also can I advance the timing to 10' BTDC as again some people have done. The reason I am trying to set this up myself is because the local LPG fitting garage want £95 to check and set it up, would it be better to let them do this after I have fitted the new parts? Cant carry on with milage like this, I dont rag it or do any town driving so I would expect better fuel economy. Any advice much appriciated cheers.

redneck way for lpg is large brass screw on most vapourisers is main, small is trim and 2500-3000 valve screwed in till revs drop slightly on y piece (power valve so I'm told)


screw power valve right out then screw main valve in until it starts to stutter and trim with small brass screw
rev up and screw power valve in until revs drop slightly


Red neck at you own risk setup, remember how many turns so you can go back if not happy with it

as you are playing with the gas system you will in validate the cert of compliance for the gas system which means in the event of a incident you will not be insured!
if you do it yourself then you will need to have the system recertifacted

I'm only trying to tweek it for better fuel economy, not overhaul the whole system. So it looks like it has got to go to the garage for setting up then.

the leonardo (aeb 175) if thats what you have should have a port for connection to laptop. i reckon someone has taken out the stepper motor and replaced it with a redneck power valve!!!

you could reset the system by adding some of this.

HNO3 + NH2SO3H → N2O + H2SO4 + H2O,run it through the syatem flat out on the motorway.

all will become after that.

that's NOX btw

or is it laughing gas

Regarding the timing...
I marked my dizzy with a stroke of tipex at the base so as it showed where the timing should be. Just line the marks back up after moving it.
Then I advanced the timing for gas about quarter of an inch clockwise and it ran a lot better.
My single point system gives between 9 and 12 to the gallon (pricewise) but that is 50% town driving.
It's a 3.5 on carbs btw.
It dosn't seem to matter how I drive it, the mileage is still the same.

I only use a light throttle when warming up on petrol as the timing is over advanced and just leave it set for gas.

My single point system gives between 9 and 12 to the gallon (pricewise) but that is 50% town driving.
It's a 3.5 on carbs btw.
It dosn't seem to matter how I drive it, the mileage is still the same.
(quote)

Had single point LPG fitted (by an approved installer) to a 3.9 a few years ago, never bettered 14mpg even on a long run with a light foot. 22mpg on unleaded.

10 MPG would be respectable if you live in a hilly area like here, or if you have a lead boot, or both - most we ever got was 21mpg on a motorway run (steady 80ish with a tail wind) the worst was 6mpg when we were pushing nearly 70mph up a 1 in 2 hill that is about a mile long and a fair bit more on the flat. That was on LPG, can't tell you the figures on petrol, as we never measured it and don't have the disco anymore.

Well just to update. I changed the dizzy cap, rotor arm, vacuum advance, new plugs, thermostat and took it to a local LPG fitting garage for setting up. And I am now getting around 16 MPG instead of 10 MPG. Well chuffed at that.