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 Post subject: oMVL lpg problems
PostPosted: Thu Apr 04, 2013 5:38 pm 
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Joined: Tue Apr 13, 2010 8:58 am
Posts: 14
Hi all a couple of problems with my LPG set up and would appreciate some advice.
The engine is a 4.2 rover V8 on twin SUs freshly installed runs okay on petrol al being a bit rich probably because the needles are worn.

LPG is an open loop OMVl R90 vaporiser.

Ignition is megajolt running on a standard petrol map.

I have a old analog air fuel ratio meter that I can use whilst driving to see the state of tune. I have been tuning it to stoich on tick over with the bypass at about 2 turns out and using the diaphragm adjustment then adjusting the in line valve to tune in whilst driving.

2 problems one is starting if it stalls which when offloading happens its a pig to start it spins over for about 30 secs or more before begrudgingly starting this is not good on the side of a dodgy hill The other problem is if I connect the raised air intake the revs go through the roof. If I the tune it with the snorkel on it stalls at junctions.

Any suggestions would be good thanks
Mick


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 Post subject: Re: oMVL lpg problems
PostPosted: Thu Apr 04, 2013 7:39 pm 
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Joined: Wed May 23, 2007 5:51 pm
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Location: Wiltshire
texpis wrote:
I have a old analog air fuel ratio meter that I can use whilst driving to see the state of tune.

Be sure to take account that desired ratios are different for LPG; ratios intended for petrol use must be translated. Lambda values will be okay as is. All depends what your meter shows or what adjustments it allows.

texpis wrote:
problems one is starting if it stalls which when offloading happens its a pig to start it spins over for about 30 secs or more before begrudgingly starting

Yup, that's the problem with basic mixer systems. After stall, the contents of the gas pipes/vaporiser spill into the manifold, effectively flooding it.
"OK start" devices counter this by allowing the engine to run on a few seconds after switching off to consume the gas.
"OK start" devices cannot fix it in a stall situation; there is no fix.
Best you can do is minimise the hose volume, absolute minimum between solenoid valve a vaporiser, and use a gas switch or safety relay that minimises the time the solenoids remain on after RPM vanishes. You do have a proper gas switch or standalone "safety relay"?

texpis wrote:
The other problem is if I connect the raised air intake the revs go through the roof.

Yes, as you've already discovered you must retune if you add restriction to the air intake.

texpis wrote:
If I the tune it with the snorkel on it stalls at junctions.

Ram air effect - discard or turn around any 'scoopy' snorkel top.

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 Post subject: Re: oMVL lpg problems
PostPosted: Thu Apr 04, 2013 7:48 pm 
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Joined: Tue Apr 13, 2010 8:58 am
Posts: 14
hi and thanks for the reply the meter shows lpg and petrol so okay with that.
Yes I have a safety relay just replaced it after intermittent cut outs that's okay now, it's the stall situation that's the problem is switching the gas of to start a better idea?
The snorkel is a strange one I had what I thought was spot on tune with the snorkel facing backwards but it stalled at junctions very time. Tuned it without the snorkel and no stalling.

Mick


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 Post subject: Re: oMVL lpg problems
PostPosted: Thu Apr 04, 2013 8:51 pm 
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Joined: Fri Oct 21, 2005 7:56 pm
Posts: 2593
Location: North Wales
I would suggest you screw the bipass back in and just use the idel screw to set the idle.

I have come across the problem with the snorkel on one car and was not able to solve it without removing the snorkel. Some snorkels are ok if facing backwards. Snorkels are the one case where the Bloss might actualy work and help with the stalling??

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