What pressure should a Single point vapouriser/reducer be set to?

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CNG
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What pressure should a Single point vapouriser/reducer be set to?

#1 Post by CNG » Fri Jan 31, 2020 11:05 pm

I would guess there's a max-min pressure tolerance exiting vaporisers/reducers. I would think multi-point systems require higher pressures. I'm rebuilding a OMVL 89e, which is much like its LPG cousin, OMVL 90e. There's no info anywhere on setting the low-pressure lever height. Better I use a manometer anyway. For fear of turning this into the next Tooless thread:

1) What's the pressure?

2) Which way do i tweak the bar to increase/decrease? I'm assuming bending the bar towards the membrane increases pressure?

3) Does a BLOS need more pressure than say, a cooker-ring or stepper-motor closed-loop system?
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Re: What pressure should a Single point vapouriser/reducer be set to?

#2 Post by Gilbertd » Sun Feb 02, 2020 12:21 am

Pressure would be fractionally below atmospheric so the gas has to be sucked through by the venturi in the mixer (I assume a Blos does the same, never played with one and consider they just add complication over a ring mixer) rather than blown in. On the 90e you don't bend anything, the pressure is adjusted with the larger of the two screws (the one with the spring behind it) which sets the pressure by acting on the lever. The smaller screw (the tapered one), is an idle bleed to allow a constant flow irrespective of the amount of suck from the mixer and dribbles a small amount of gas through to keep the engine running at idle if there is insufficient suck.
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Re: What pressure should a Single point vapouriser/reducer be set to?

#3 Post by CNG » Sun Feb 02, 2020 3:18 am

Thank you Gilbert. I did wonder about a BLOS over a cooker-ring. I am hoping to have a closed-loop stepper-motor feed the BLOS to avoid a cooker-ring. But before I complicate it further with a stepper in there, better it run solely on the BLOS.

I'm struggling to get the mixture rich enough. It has always been like this from install and I'm now putting time into looking at it properly. The BLOS sits upstream of an SU, and the SU was full of vacuum leaks which I've smoke-tested and cured. The throttle spindle, float-bowl air-venting etc. I thought that would cure it. I battle on.

Installed using the one, now I've tried both 19mm outputs (top and bot) from the OMVL feeding into the BLOS and it helps, but my O2 gauge still indicates weaker than stoich. I've seen the two adjustment-screws. The idle is half-turn out, and the coarse I call this the 'float-level' sits out as far as it goes. Still runs weak. It's only a 2.25 petrol Land rover and whilst as juicy on liquid (18 mpg) as many 5.0L engines, I'm reckoning the OMVL has capacity. So perhaps it's an adjustment issue? This leaves two questions. I'm still puzzled:

1) Is the BLOS asking for enough gas? Or..
2) The OMVL is not supplying it?

I'm confused by your suggestion about negative presssure. The OMVL will output positive correct? To meet the negative demand? I think I need more 'suck' from the engine, and thought the vacuum leaks (which were tiny) were the root of why I'm not getting it. A BLOS comes with three 'needle' options, and I've the richest in there.
My attack plan is to be sure OMVL is putting out enough gas, the fact that two feeds helped makes me think it doesn't. The OMVL factory rebuild does talk about bending levers, but in typical Italian style, neglects to say which way, or give a height. Or a pressure.

I realise this will be an ongoing tail-chase of ignition timing (I have programmable ignitiion) and fuelling. At the moment I want to be able to get the thing to run rich, as well as weak. No amount of tweaking will make it do this.

Then I can look at the wider picture and get it sweet.

Which way do I bend the bar for increase? Once I've got that right, I'm thinking to short-circuit the BLOS, 'nail' a cooker-ring on there, and/or stepper.

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Re: What pressure should a Single point vapouriser/reducer be set to?

#4 Post by CNG » Sun Feb 02, 2020 9:33 am

The reason I point my finger at the OMVL is that lifting the BLOS piston does not stall the engine until it's near WOT. ie the gas-supply does nto increase.

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Re: What pressure should a Single point vapouriser/reducer be set to?

#5 Post by Gilbertd » Sun Feb 02, 2020 11:01 am

If it were me I'd remove the complication and fit a cooker ring mixer between the carb and manifold. That way the carb is doing nothing other than providing a throttle butterfly. Usual settings on an OMVL are bias around the middle of it's allowed movement and the idle bleed screwed fully home. Screwing the bias out increased the pressure, in reduces it. With the Blos you've got the symptoms of a too large mixer so will generate insufficient 'suck' to draw in enough gas. Opening the idle bleed screw will compensate for this by dribbling extra gas in permanently, but will have no effect at all as soon as you open the throttle, the tiny amount of additional gas isn't enough to keep the mixture correct. There's a good explanation her http://www.diy-lpg.co.uk/articles/files ... -loop.html if you haven't seen it.
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Re: What pressure should a Single point vapouriser/reducer be set to?

#6 Post by CNG » Sun Feb 02, 2020 8:31 pm

Thank you G. I can see your thinking re: insufficent 'draw'. I had a BLOS was there to prevent exactly that. It's a variable venturi much like the SU sitting down-stream. Which sets me to thinking I should remove the SU piston just to see it's causing the vacuum loss you speak of?

Or instead of me putting ever-richer hi-flow BLOS needles in there, perhaps I should go leaner? I'll not give up the fight yet, but a cooker-ring becomes default I think.

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Re: What pressure should a Single point vapouriser/reducer be set to?

#7 Post by CNG » Mon Feb 03, 2020 5:12 am

Just read this wrt BLOS:

Please note: a positive pressure vaporizer is required for proper operation. Works with Airod vaporizers. Does not work properly with Impco vaporizers.

I am correct in thinking the installed OMVL 90e / 89e is a 'positive pressure'?

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Re: What pressure should a Single point vapouriser/reducer be set to?

#8 Post by Gilbertd » Mon Feb 03, 2020 9:50 am

Not the way I read it, it's at atmospheric 0±20 Pa, see https://www.lpgteile.de/intern/809100_0 ... Manual.pdf
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Re: What pressure should a Single point vapouriser/reducer be set to?

#9 Post by CNG » Mon Feb 03, 2020 10:37 am

Thank you G. If you're right, and you appear to be, and

"a positive pressure vaporizer is required for proper operation."

Is also correct, that'd be why, whatever I do, I can't get it to supply enough gas. Thus, I've the wrong reducer for a BLOS. But I'm puzzled. In many V8 Land rover threads a OMVL 90e (agreed in LPG flavour) appears the weapon of choice with a BLOS. Reg OMVL bumpf for 90e also reads atmospheric 0±20 Pa.

I need to do more digging. Find out which are +ve pressure and by what degree.

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Re: What pressure should a Single point vapouriser/reducer be set to?

#10 Post by Gilbertd » Mon Feb 03, 2020 11:11 am

Is that using a Blos instead of an SU rather than as well as though? The R90e works perfectly on a V8 with a mixer, although I've never owned a pre-EFi Land Rover, I gave up on carbs about 20 years ago and much prefer fuel injection. Like I say, I've no experience with a Blos and prefer to keep it simple with a mixer and lambda feedback rather than add more complication.
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Re: What pressure should a Single point vapouriser/reducer be set to?

#11 Post by LPGC » Mon Feb 03, 2020 11:28 am

Can't help with bending of arms etc inside the R89 reducer... the best people to answer that are probably TinleyTech but I'm not sure how much help they'll be able to give. On an R90 you can probably effect the same things as bending the arms using the adjustment screws.

R90s (and other mixer system reducers) supply gas at very close to atmospheric pressure.. if they supplied much positive pressure it would cause the engine to run way too rich at idle, negative pressure would cause the engine to run way too lean mostly effecting idle (presuming correctly sized mixer).

The Blos should be used with a standard type mixer system reducer (so such as the R90), not a reducer that provides constant positive pressure (so unlike a sequential system reducer and unlike some of the Impco gas carb reducers). The idea of the Blos is that it gives a variable size inlet orifice depending on airflow much like an SU carb but still pretty much relies on the venturi effect like a mixer (unlike a gas carb)... marketing suggests it can give 'many times the suction of a traditional mixer at low engine loads' - if that's correct it would suggest the reducer sensitivity may need to be set lower than for a traditional mixer, but the Blos does have it's own adjustment screws and in practice a middling position of the reducer sensitivity screw is usually set. TT would advise on setting up the Blos too. Like Gilbert I too think they're an extra (and usually unnecessary) complication but they can give great results if set up well.

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Re: What pressure should a Single point vapouriser/reducer be set to?

#12 Post by CNG » Tue Feb 04, 2020 10:10 am

When not one but two LPG pros aren't as happy with the BLOS other accounts would suggest, my resolve to get this thing working weakens. Posts form both of you make this site what it is. Dai is good too, but not seen him on for a 'whiles'. If you were nearer, I drop either of you a few hours labour to looksee.

The OMVL 89e is the CNG version of their 90e. Same casting, excepting the high-pressure front-end, they're the same product. And there's Chinese copies of both. See piccy. Both of you seem to think messing with levers won't help because it's not more pressure needed here, it's more gas. Which is not quite the same thing. i need to work out why I'm not getting more gas.

I've been chatting to Mick at TT, and he's very good about it. Not got to the bottom of this yet, I've two cooker rings here, ready to go on.

A) An SU carb version - sits on carb but is restrictive.
B) A larger 70mm bore job. Same diam as BLOS.


Wondering if B will provide enough vacuum or give me much the same problem, but easier to fit - it goes on first.
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Re: What pressure should a Single point vapouriser/reducer be set to?

#13 Post by CNG » Tue Feb 04, 2020 10:23 am

A thought, I did have vacuum leaks, at SU float-bowl vent, and throttle-spindle, these now cured. Have I placed the BLOS too far away from the manifold, thus to an extent explaining lower vacuum? Not my install, but much the same. My pipe (seen orange here) is 3" shorter, but with my 'U' fitting, could it be that it's still too far to go?
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Re: What pressure should a Single point vapouriser/reducer be set to?

#14 Post by Gilbertd » Tue Feb 04, 2020 10:35 am

That looks horrible and you've got an enormous quantity of fuel vapour ready to go bang at the slightest hint of a misfire too. Just fit an SU mixer between carb and manifold. As you'll be able to run on gas from stone cold, you don't even need to worry about turning the petrol flow oiff and running the carb float chamber dry before the gas kicks in. Fitting a large mixer will have much the same affect as you have at the moment. I bought a 4.6 P38 Range Rover with a singlepoint Leonardo system already fitted but not working. Previous owner had spent a fortune on it so it had a brand new R90e and stepper but while I could get it to run at idle, it went ridiculously lean as soon as I opened the throttle and died on me. Turned out that the middle of the mixer was missing! As TT are not far from me, called in there and got a 36mm mixer which is what they would normally supply for a 4.6 Land Rover V8. Spent ages trying to get that to work and still went lean at open throttle. Checked my 4.0 litre Range Rover and found it had a 34mm mixer so swapped that over to try, perfect. Went back to TT and got a 34mm, fitted that and it was spot on. Although the theory says that a small mixer will give too much restriction in practice it is barely noticeable as the airflow through the venturi accelerates it so you still get much the same quantity of air going in.

I'm not a pro by the way, just someone who has a habit of buying cars that are advertised as spares or repair, only ones that already have LPG fitted (which invariably isn't working) and have re-engineered them to my standards and got them working properly.
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Re: What pressure should a Single point vapouriser/reducer be set to?

#15 Post by CNG » Wed Feb 05, 2020 1:58 am

Not a pro? Your words come across well enought to give that impression. As I said, that's not mine. However... if you don't like the look of that offering, you'll not see mine as any better. Other than putting BLOS in front of the SU, can't see any way to answer your critique. I'm fed-up fighting this one. I shall stick a cooker-ring twixt SU and manifold. It'll affect WOT I suppose, only who am I kidding? What I have now works so well...

I'll beat this b*&5^7d if it kills me.

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Re: What pressure should a Single point vapouriser/reducer be set to?

#16 Post by Gilbertd » Wed Feb 05, 2020 9:14 am

The definition of a professional is someone that gets paid to do something, whether he does it properly or not is a different matter. I'm just a qualified engineer who understands how something should work but work on my own vehicles without getting paid for it......
96 Saab 900XS, AEB Leo, sold
93 Range Rover 4.2LSE, Lovato LovEco, sold
97 Range Rover 4.0SE, multipoint, sold
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96 Range Rover 4.6HSE Ascot, AEB Leo, my spare


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Re: What pressure should a Single point vapouriser/reducer be set to?

#17 Post by LPGC » Wed Feb 05, 2020 10:11 am

TinleyTech will probably be able to supply you with a special type mixer that's purpose designed to bolt onto your model of SU carb and allow the inlet ducting to be refitted (i.e. not a generic mixer and not round like a normal mixer). Thinner than a normal mixer so (regards your pic) would likely allow the curved metal inlet ducting to fit without fouling against the vehicle body / heater box.

That said, I would expect the Blos to work in the position it's in in the pic. As Gilbert said, not ideal because there's a fairly long distance between the throttle body (carb) and mixer but you've said that on your own car that distance isn't quite so long (the orange pipe is shorter). You're using a reducer that is at best suspect, can't say if you've even rebuilt it properly etc - If I was in your situation and still wanted to go with the Blos what I'd do is park another car fitted with an LPG mixer system alongside it and rig it up so the other car's reducer fed your car's Blos with LPG. This would at least allow you to see the Blos running your engine and run some minor tests such as how it responds when blipping the throttle etc.. not all inclusive tests and things would be a little different (and have to be set up a bit different) for running on CNG but would expect those differences to be able to be fairly easily accounted for by adjusting the Blos and reducer when you're back running on CNG.
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Re: What pressure should a Single point vapouriser/reducer be set to?

#18 Post by CNG » Fri Feb 07, 2020 9:24 am

As I said, set with two forms of cooker-ring. I used to run LPG so have all manner of stuff knocking about.

1) 70mm jobby - fits to intake pipe.
2) SU HS6 specific (will fit as you suggest).

I'll keep the intake tract short. Frankly, whilst not very pretty, I hadn't seen the issue until pointed out by both of you. Thank you.

Life gets in the way, yet I'm set to try both this weekend. I like the idea of getting another car to eliminate one end. If the 'SU HS6 specific' doesn't do it, it's a deeper issue. I have Innovate O2 gauge in there, which is overkill, but watching the AFR helps a heap. I'm usually pretty good at this sort of thing, I like to think I know what i'm doing. This set-up couldn't get much more basic, hence I'm ashamed to admit this beats me. I WILL get this if it kills me.

I suspect this will finish with a stepper in there somewhere. Won't leave this thread like so many do, without conclusion. Will report back.

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Re: What pressure should a Single point vapouriser/reducer be set to?

#19 Post by CNG » Fri Feb 14, 2020 12:13 am

Today I tried my two cooker-rings. Made things worse... BLOS was better.

1) 70mm cooker-ring - It's a bit large, but used to run LPG thu' it and running the same engine. Now will barely run over idle. Part-choked off inlet with a rag, then it'd rev to peak. Mixture actually rich at idle, soon weakens (on O2 gauge) if I revved.
2) SU dedicated cooker-ring, pretty much ditto of the 70mm

To my way of thinking that says the BLOS is fine. It perfomed better than the cooker-rings, which is what is supposed to a happen. If a cooker-ring doesn't cure this, I need to look at my reducer. Which puzzles me, I've two here which I tried earlier, neither cured the issue. Now to look deeper...

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Re: What pressure should a Single point vapouriser/reducer be set to?

#20 Post by CNG » Tue Feb 18, 2020 9:11 am

Been a few days. Well I can't quite believe this, but I've got it to work. Only I'm not convinced I know why. Having put every mixer under the sun on the thing, and failed, I then swapped the reducer. No improvement. Still ran weak. I thoiught to hell with it, I've got the choice of every single-point mixer here, I'll try two. I cobbled-up two BLOS, yes two, and yes in series.Now it works? But why?

OK, now the damned thing runs slightly rich, and it looks er... frightening. Gilbert, you will not be impressed. But it works? I'll post pix, yet that's a K&N, followed by two BLOS (one feeds the other), one SU.... then the manifold, and this abortion works? It's an inlet-tract a mile long. The BLOS mixer(s) - singular or twinned - run the best, yet still not well. I think it's a suction issue. I only hit on the idea because thumbing thru' BRC's catalogue, there's even a gizmo to counter low suction. However suction doesn't seem to explain why two choices of one cooker-ring won't work, but two BLOS in-line does.

Deep shame, vainly attempting not to duplicate the Tooless thread`;

viewtopic.php?f=33&t=8148

Mind, perhaps I shouldn't shy away from such things, 'tis internet-gold.

I sit a tad reticent to post pix of what I now christian "The Thing' but it works? It's never run that well, and I've simply lived with it. Making it my mission to solve this, I think I've got to the bottom of it - runs better than it ever did.


When I've tidied this mess, reckoning on a AEB Leonardo, or the later (and cheaper) Galileo in there. AEB don't make the Leonardo, but OMVL still sell it as the Millenium? Odd. Before I get to that, I need to solve the rich running. I hope weaker BLOS needle(s) and/or a power valve will help.

I carry on digging.
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