SLROC Forum

My LPG-powered Lightweight is running really nicely but using more fuel then it ought: down from 4 miles/litre to about 3. I'm guessing that it's running rich, since I got a new regulator valve fitted (and tuned) recently, but

* What else should I be checking?

* What is the best way to adjust the mixture? My current plan is to experiment with different settings on the mixture screw, driving up the same hill to see which mixture runs best, but is there a better way? I have a vacuum gauge if there's some way to use that.

I got it serviced recently, so one would hope that tappets and the like are correct. And I've checked the timing; it's good.

Best way is to put it on a gas analyser with someone who knows where the figures should be for LPG. It could be running very lean which does cause high consumption too oddly enough.

Cheers for that. Anyone able to recommend somewhere in the Edinburgh area? (The original conversion was done by Wellside Motors in Kinross, but their gas analyser broke and they haven't replaced it.)

Last night's update:

I had a play last night, using a vacuum gauge and a (shiny new) colourtune.

The existing setting was with the regulator valve unscrewed by 3.5 turns. The vacuum gauge showed a good, steady vacuum; the colourtune showed a blue flame with a yellowish tinge, and which flickered yellow.

At 3.25 turns, the flame was less yellowishand with had less yellow flickering.

Between 3 and 2.75 turns, both vacuum and revs dropped off significantly.

All the above was true at tickover, and also with the choke pulled fully out (on LPG the choke increases the tickover speed but does not affect the mixture) and the headlights and 40A radiator fan turned on to try to put a bit of load on the engine.

I then tried driving up the same hill with my foot flat to the floor, with the regulator valve set at various values between 3.5 and 2.5 turns. And I found no significant difference! Passing my first marker at 40MPH, it would either do a steady 40 or accelerate to 41 or maybe even 42MPH on the steep part of the hill, then after the hill levelled off it would accelerate to between 50 and 52MPH by the time it reached my second marker.

So, I've set the regulator valve to 3 turns (i.e. I've made it more lean by half a turn), and shall monitor fuel consumptiuon at that setting.

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Are they good? Used to live a mile from there for 3 years and never (needed) went in. Would be good to know if they know what they are doing as there are a lot of grey areas with LPG.