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Tuning a V8 for LPG and Petrol


Fatboy
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Ladies and Gents,

I am sure that I've read an excellent thread on the optimum plugs and timing settings for the V8 to run on either LPG or Petrol but I've searched and can't find it on here or "there". (I thought it was Fisha that was involved but as I've said, can't seem to find it! :( )

IIRC, it gave an excellent step by step instruction on how to set up a OMVL LPG system with Ecomax and Max Flow Adjuster (which is exactly what I have).

I have also been tearing my hair out for the past couple of days because I cannot get "her" 90 to run right on both fuels (one at a time obviously ;) ).

Now, it may be getting complicated by the RPI Power Amp... which I suspect is "iffy".

On LPG, with timing set at 12 deg, she runs very well. No pinking, good power.

On switching to petrol, (therefore timing should retard via Power Amp), the rev counter becomes all flickery and tickover is too high (1200rpm). Carbs have been stripped and cleaned). checking the timing shows it seems to be erratic and very close to zero. (Rev counter is fed off coil).

Another observation is that the temp guage is reading low on both fuels but god knows if this has any influence on this problem.

From what I can remember, the RPI Power Amp is set on LPG. When you switch to petrol, it retards the ignition to the optimum setting. It also amplifies the spark.

The IWEMA black box is kind of opposite - It is set on petrol and then advances the timing when switched to LPG.

I though that the RPI system sounded like it would have less strain on internal components because its base setting is on the fuel which I run the most (LPG). However, there is a difference in build quality and I'm more inclined to think the IWEMA box looks better.

Opening up the RPI box last night and I could see some fur on some of the soldered joints - Should I work round these with the soldering iron just incase there is a dry joint? Can I hose the thing out with WD-40?

Any help gratefully appriecated :D:D

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could you post a piccie of the insides? always difficult to say yay or nay on rework without looking at it.

i'll put together a quickie bodge it guide to setting up the mix on an OMVL R90 vapouriser . . . . but i'm not 100% sure about the ecomax thing . . .

Edited by fisha
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Ladies and Gents,

I am sure that I've read an excellent thread on the optimum plugs and timing settings for the V8 to run on either LPG or Petrol but I've searched and can't find it on here or "there". (I thought it was Fisha that was involved but as I've said, can't seem to find it! :( )

IIRC, it gave an excellent step by step instruction on how to set up a OMVL LPG system with Ecomax and Max Flow Adjuster (which is exactly what I have).

I have also been tearing my hair out for the past couple of days because I cannot get "her" 90 to run right on both fuels (one at a time obviously ;) ).

Now, it may be getting complicated by the RPI Power Amp... which I suspect is "iffy".

On LPG, with timing set at 12 deg, she runs very well. No pinking, good power.

On switching to petrol, (therefore timing should retard via Power Amp), the rev counter becomes all flickery and tickover is too high (1200rpm). Carbs have been stripped and cleaned). checking the timing shows it seems to be erratic and very close to zero. (Rev counter is fed off coil).

Another observation is that the temp guage is reading low on both fuels but god knows if this has any influence on this problem.

From what I can remember, the RPI Power Amp is set on LPG. When you switch to petrol, it retards the ignition to the optimum setting. It also amplifies the spark.

The IWEMA black box is kind of opposite - It is set on petrol and then advances the timing when switched to LPG.

I though that the RPI system sounded like it would have less strain on internal components because its base setting is on the fuel which I run the most (LPG). However, there is a difference in build quality and I'm more inclined to think the IWEMA box looks better.

Opening up the RPI box last night and I could see some fur on some of the soldered joints - Should I work round these with the soldering iron just incase there is a dry joint? Can I hose the thing out with WD-40?

Any help gratefully appriecated :D:D

Hi Fatboy,

This should be of use to you:

http://www.cunningham.me.uk/rangiewiki/ind...OMVL_Adjustment

If you are not sure whether your RPI amp is the cause of the problems on petrol, I would revert to the standard ignition system (without the RPI amp) and set the timing to 6 degrees(or whatever standard spec for your model is in petrol) at idle and see what happens on petrol. If it runs poorly, then you need to get it running correctly before retrying the RPI amp, or you may be chasing a fault you don't have.

Hope this helps,

Regards,

Diff

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Minivin,

I'll get a photo tonight.

Don - I don't expect you to write something new, but I'd be grateful for the notes you posted before.

Diff - Thats a good start!

Cheers Gents! :D

I'm ashamed to say that I had not actually though of taking the RPI Amp out of the loop and trying on petrol with the old coil :rolleyes: I will give it a go.

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From what I can remember, the RPI Power Amp is set on LPG. When you switch to petrol, it retards the ignition to the optimum setting. It also amplifies the spark.

The IWEMA black box is kind of opposite - It is set on petrol and then advances the timing when switched to LPG.

Correct, the IWEMA one works differently but I am not 100% sure how as I have not used one.

Have spoken to a couple of "independants" who have used both and they both preferred the IWEMA. There was some failures with the early RPI ones but I believe they honoured warranties and the problem as a manufactuirng issue that has been resolved.

Edited by Niall_CSK
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>Now, it may be getting complicated by the RPI Power Amp... which I suspect is "iffy".

I have both the RPI one and the Iwema one.

The issues with the RPI one are entirely down to ingress of moisture. Try sticking it in the airing cupboard for a couple of days and you'll probably find it has come back to life.

I found that by relocating it so it is screwed to the heater on my 90 and filling the inside of the box with silica Gel - it was much better.

The Iwema one I found a lot more difficult to persuade to work - it depends upon your distributor. The RPi one has an ampligier for the pickup in the distributor so it works without the amplifier pack normally fitted between the distributor and coil. The Iwema one requires the amplifier or a distributor with mechanical contacts - but gets upset if the amplitude of the signal out of the amp is too high (it was firing on the leading and trailing edges of the pulses causing misfires and 'random' timing).

I have wound up going back to a regular electronic ignition pack - actually from a rover car. It generates a much better spark than either the RPi or Iwema, it's a potted pack with spade terminals so no chance of water ingress and although it neither advances nor retards, mine now runs better than it ever did on either the RPi, Iwema or original LR components.

I'm sure this is a bit like the way that painting a line down the side of your car makes it go faster. Best advice - keep it simple.

Si

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