Thread: LPG Mileage

You are most likely burning the gas. a leak of significant size would be easy to spot by the big frosty patch developing around it. Try finding the main mixture adjuster, mark its current setting, then try a leaner setting for a while. Test drive after the adjustment, you can always go back to your marked setting.

For optimum economy you should have an O2 sensor and LPG processor fitted, parts cost is around $300. They usually save between 10 and 20% of your fuel use in a normally tuned engine.

Hi, what's your timing set at? I have a 12/96 d1 same setup,since kicking the timing to 10 deg BTDC it helped heaps, my only set back is it now holds a high idle 1500 rpm for a little bit before settling. Down to normal ...Gary

Thanks guys,I will have a play with the mixture setting.Regarding the timing,I have the higher compression engine so have set the timing back a little at 6 deg BTDC.What mileage should I be looking at on LPG ?
Cheers
Shane

Originally Posted by mandala1111

Thanks guys,I will have a play with the mixture setting.Regarding the timing,I have the higher compression engine so have set the timing back a little at 6 deg BTDC.What mileage should I be looking at on LPG ?
Cheers
Shane

What compression ratio? Does it "ping" or detonate under load? Your fuel consumption should be around 20-25 l/100km but this really depends on the terrain. If it is burning 100% cleanly you should be able to wipe your finger in the tailpipe and have it come out clean, not sooty. Note: to do this test you must clean the tailpipe, don't run on petrol at all, and do a tank full. There should be no new soot deposits from excessive fuel burning. Your engine can be 25% richer than optimum without losing any power. Best economy will lose a small amount of power unless you have that processor installed.

Originally Posted by bee utey

What compression ratio? Does it "ping" or detonate under load? Your fuel consumption should be around 20-25 l/100km but this really depends on the terrain. If it is burning 100% cleanly you should be able to wipe your finger in the tailpipe and have it come out clean, not sooty. Note: to do this test you must clean the tailpipe, don't run on petrol at all, and do a tank full. There should be no new soot deposits from excessive fuel burning. Your engine can be 25% richer than optimum without losing any power. Best economy will lose a small amount of power unless you have that processor installed.

Thanks Bee utey,I have just set timing at 10 deg BTDC and wound in the mixture a bit.Just took it for a drive and I have a little more power.I will see how things go.The gas system is an Impco mixer type so when setting the mixture manually is there a rough guide as to where to set it to.If I wound the mixture screw in all the way then where would be a good starting place to set it to from there ? I have a lot of experience tuning an engine on fuel but I am a bit lost when it comes to LPG so thanks in advance for any guidance.

Originally Posted by mandala1111

Thanks Bee utey,I have just set timing at 10 deg BTDC and wound in the mixture a bit.Just took it for a drive and I have a little more power.I will see how things go.The gas system is an Impco mixer type so when setting the mixture manually is there a rough guide as to where to set it to.If I wound the mixture screw in all the way then where would be a good starting place to set it to from there ? I have a lot of experience tuning an engine on fuel but I am a bit lost when it comes to LPG so thanks in advance for any guidance.

Hehe, on an Impco what you have done is wind in the idle mixture screw (which is an air bypass screw), making it richer. It should even have the word "idle" cast next to it, with an arrow for adjustment direction. The main mixture adjuster is a small cam on the gas inlet to the mixer marked "L" and "R" with some marks in between. Move the cam one mark towards "L" and see how it goes.

Basically your Impco is like major restrictor in the inlet at low speed, you need more hoof to get it going so you lose the vac advance under even light load. Advancing as you have done should help correct that.

Originally Posted by bee utey

Hehe, on an Impco what you have done is wind in the idle mixture screw (which is an air bypass screw), making it richer. It should even have the word "idle" cast next to it, with an arrow for adjustment direction. The main mixture adjuster is a small cam on the gas inlet to the mixer marked "L" and "R" with some marks in between. Move the cam one mark towards "L" and see how it goes.

Basically your Impco is like major restrictor in the inlet at low speed, you need more hoof to get it going so you lose the vac advance under even light load. Advancing as you have done should help correct that.

Thanks again bee utey,I have now adjusted the idle screw to where the engine idles nicely and then just out a little tweak more.Also I found the mixture cam and it was sitting dead centre so I have tweaked it 2 marks towards L.I am going away on a nice trip today for a few days and will see how things go.One question though regarding mixture,I spoke to a mechanic friend yesterday and he suggested to make the mixture a little on the rich side,his theory is that with a richer mix you can be a bit lighter on the pedal due to more power so therefore using less gas this way,what do you think about this ? Also my engine has a 9.35 compression ratio and it does not ping,it is running very smooth and quiet.
Cheers
Shane

Originally Posted by mandala1111

Thanks again bee utey,I have now adjusted the idle screw to where the engine idles nicely and then just out a little tweak more.Also I found the mixture cam and it was sitting dead centre so I have tweaked it 2 marks towards L.I am going away on a nice trip today for a few days and will see how things go.One question though regarding mixture,I spoke to a mechanic friend yesterday and he suggested to make the mixture a little on the rich side,his theory is that with a richer mix you can be a bit lighter on the pedal due to more power so therefore using less gas this way,what do you think about this ? Also my engine has a 9.35 compression ratio and it does not ping,it is running very smooth and quiet.
Cheers
Shane

You can adjust your particular system for EITHER best economy, OR best power, not both at the same time. Best economy is at about 20% less mixture than best power. The idea being that if you use 20% less mixture and lose 10% power at full throttle you are still ahead. Without a dyno and quality time spent changing your mixer characteristics you have only one adjustment for economy on the road. Go drive it and see how it feels. Old mechanics' theories aren't all they are cracked up to be. The reason that electronic mixture controllers rule in the modern era is because they can do both power and economy as needed, and you don't have one.