Club 80-90 Forums

During my hot trip in France, and on a long flat part, it was observed that the engine running temperature increased slightly on LPG.
At 70 mph the temp indicated "12.00" on the guage or the needle covering the led.
I had noticed this before, so as the road was long and flat I switched to petrol.
This resulted in the gauge needle falling back by "half an hour" to just touching within 5 mins.
It doesn't do this below 55 and stays the same as petrol.
As expected the oil pressure dropped by 0.5 bar when the temp increased.

Would this indicate a weak gas mixture at higher rpm?

Yes running too lean , or timing out 

Yeah I thought so too.
So I got it checked on a gas analyser and it read .95 on the Lambda reading at idle.
Which seems pretty much ok.
Timing at 10 deg btw.

Very odd.
I thought there may be another reason.

idle reading doesn't show how it's running at revs, probably need to balance the vaporiser idle setting and the powervalve setting which really can only be done under load in real world driving situation, I remember stories of M0cki adjusting someone's set-up whilst the van was being driven; if you have a millenium type set up the map might need adjusting I guess, obviously Andrew can advise much better, I only had an open loop set up so was reliant on Steve's (RIP) experience and my experience driving it to get a decent balance that didn't harm the engine, but that good driveable balance never gave better than 19.5mpg, but gave a consistent 16 minimum and 18 average, Syncro MV on 205s

That's interesting. This might help us understand it, rather than my wafflings:
https://fuelsforum.rasoenterprises.com/ ... php?t=1640

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Assuming it's Blos, a simple test would be to just richen it up by a quarter turn of the outer ring and retest up the motorway.

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Yes I did do that , on more than one
That was with the twin “power valve” on a gas ring ( long before Blos) and it served to get maximum power under load whilst giving economic running under normal circumstances.
Normal set up with both adjusted to get correct mixture at tickover and then only giving the secondary valve more when the second half of the carb opened

No rolling roads with in the pay grade in them days !

Steve didn’t like that approach, but it brought the power up and kept the economy equal to petrol and ensured it wasn’t too lean when under big load

No need these days with Blos doing the job

ajsimmo wrote: ↑24 Aug 2020, 09:25 Assuming it's Blos, a simple test would be to just richen it up by a quarter turn of the outer ring and retest up the motorway.

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No blos.
It's just the old OMVL open loop with two powervalves.

I ran it up to 3000 rpm and turned in the big screw on the vapouriser until it faltered then returned it a 1/2 turn.
I've never altered the valves.
I know the 2nd venturi was 1/4 turn out more than the inner.
It was set up on a 1.9 but now on a 2.1

kevtherev wrote:

ajsimmo wrote: ↑24 Aug 2020, 09:25 Assuming it's Blos, a simple test would be to just richen it up by a quarter turn of the outer ring and retest up the motorway.

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No blos.
It's just the old OMVL open loop with two powervalves.

I ran it up to 3000 rpm and turned in the big screw on the vapouriser until it faltered then returned it a 1/2 turn.
I've never altered the valves.
I know the 2nd venturi was 1/4 turn out more than the inner.
It was set up on a 1.9 but now on a 2.1

Interesting methodology. At 3000 revs the mixture may well be close to stoich, which suggests the bias is near enough, but nearer 4k (when you're doing 70) max gas flow may well be choked by the power valve. It's cruising at neutral throttle when you see this happen, not WOT, so probably needs the main power valve (as opposed to secondary/ full throttle one) opening a smidge.

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how old is the vaporiser ?; the diaphragm can become baggy over time and the response then less than optimal, I had to replace the vaporiser as no amount of fiddling by Steve would get it right (mpg dropped and wouldn't improve, with new vaporiser it went straight back to where it had been once bedded in); it was cheaper to replace the vaporiser than replace the diaphragm (once labour factored in) as the vaporiser had come down in price from the cost when the system was fitted. I replaced it after about 10 years and 50k miles

Good point, Aidan. Didn't think about that, but I have replaced 2 or 3 due to being worn out, and it is cheaper to replace the whole thing.

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