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Nasty Emissions?


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I couldn't find anything on the web about how to set up your own LPG - most sites say 'take it to a grown up'.

This is what I've found from the web and from trying it out for myself. This only applies to vehicles with carbs or with a venturi mixer on the inlet.

I have one of the CO2 gas tester things from Gunson - but it works equally well with Colourtune.

On my setup there are three controls.

1. The 'Power valve' which is a screw flow adjuster in the pipe from the vaporiser to the carbs.

2. The Diaphram Tension adjuster. This is a big plastic screw on the side of the vaporiser.

3. The Diaphram bypass (or idle) screw. This is a brass screw on top of the vapouriser next to the gas outlet.

Your setup may be different, but it will still have the three adjustments.

The power valve in part controls the mixture, but also the responsiveness of the throttle and the economy.

I set the power valve first.

Unscrew the valve completly (just before the screw drops out).

Rev the engine to about 3000 rpm

Screw in the power valve until the RPM drops a little

Unscrew the valve until the revs pick up and then unscrew another 1.5 turns.

Next the diaphram tension. You only need to do this if there is not enough adjustment in the brass screw to set a proper mixture. If it needs adjusting, with the brass screw all the way in, the mixture will be rich.

Unscrew the plastic screw in increments of one turn

If the revs start to die, screw in the brass screw on the top to keep the revs up.

Unscrewing the plastic screw is richening the mixture while screwing in the brass screw is weakening it.

Continue until the brass screw reaches it's end stop (fully screwed in).

Now screw in the plastic screw until the engine just dies then unscrew it a turn or so.

Now unscrew the brass screw 1.5 turns. This should allow the engine to re-start.

If not, unscrew the plastic screw a bit and try again.

Next set the emissions by screwing in (or out) the brass screw.

On mine, it needed about a 1/4 turn clockwise to set the CO2 emissions to about 2%.

The brass screw needs quite fine adjustment. As you screw it in, the mix gets weaker and the revs drop.

It is a case of choosing an rpm high enough not to stall but with acceptable emissions.

When the mixture is good, it is worth repeating the power valve adjustment.

If the power valve is screwed in too far, when you press the accelerator, there will be a delay before it does anything and the revs will only pick up slowly.

If it is too far out, you get lightning response - but it uses loads of fuel. The 3000 rpm guide seems a reasonable compromise, but you could adjust it a little either way for power or economy.

My V8 has been a bit lack lustre on gas for a while. I tried it out on the A24 today and it went ....err...no more than 70mph (honest :) )

Although no doubt one of you grown-ups will rip this to shreds, I thought the thread could provide useful info for those not keen to shell out on getting a grown up to look at it.


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That is excellent, thanks.

My 90 was failing its MOT the other week until I tampered with every screw on it to get the emmissions down to pass. It now don't run so good.

It had previously been set up by a Green Flag chap but I'm not sure he was that au fait with all of the LPG bits (inc Ecomax).

So once I get my garage back, I'll give it a go!

Thanks again, :D

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Not going to rip it to shreds, but i'll add a couple of my thoughts....

I do the power valve after setting the initial mixture. The power valve clamps down on maximum flow, so you really want the mix to be set right with no restrictions first. Once thats done, then limit the mix's power so to speak.

but in reality, if you do a few iterations of mix and power then it'll even out.

For the sake of completness, not all vapourisers have the plastic screw. Another version of adjusters is:

1. As before.

2. The Diaphram Tension adjuster. This is a big plastic screw on the side of the vaporiser.

This is often also the larger of 2 brass screws on some vapourisers

10mm hex head on an OMVL R90e etc

3. The Diaphram bypass (or idle) screw. This is a brass screw on top of the vapouriser next to the gas outlet.

Also often the smaller of the 2 brass screws right next to the tension adjuster

8mm hex head on an OMVL R90e

IF you have one of the closed loop systems, then you should disconnect the stepper motor when it its fully open position and then to the adjustments you describe ( but leave out the power valve part ) .

once the mix is set, then plug back in the stepper motor.

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Good comments. In practice I did a couple of itterations, just because both had an effect on the CO2 reading.

People have talked about there being a filter somewhere? Any ideas where? There's nothing obvious I can see.


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There is normally at least one filter on the liquid supply line into the vapouriser, often just after the solenoid shut off valve. Depending on the make / installer it may not be obvious being inside a connection.

Just to filter solids such as rust flakes etc. it won't stop "heavy ends", nothing much will, you just need to be prepared to open and service the vapouriser 30-50k miles depending on teh quality of your local supplier.

Our local, Calor (Ayr) / Shell (Kilmarnock) / Morrisons (Kilmarnock) lasted over 60K (1600cc Astra) before a build up damaged the diaphragm, as a guide.

Good post lads.

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On my IWEMA sourced systems, the filter is in the little bowl under the solenoid on the liquid line from the tank, before the vapouriser. Its one unit (Filter/Solenoid), manufactured by EMMEGAS and whenever I've checked it, it is spotless.

Mind you, I did have a pressure relief valve lift and jam with a bit of swarf last year - That was fun :o

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