I am fitting an LPG system to a Talbot Express 2.0 and am experiencing
dangerously lean fuel mixture when running on petrol (the LPG system
has not been completely fitted yet, but I need to retain good petrol
performance). I have installed a lambda probe just below the exhaust
manifold and a dashboard Lambda gauge to instantaneously monitor Air/
Fuel (A/F) ratio. I have conducted several test runs over the same 2
mile stretch of road in various configurations and discovered the
following problem which I don’t understand.

The problem: Without the mixer in place the petrol A/F ratio is
perfect and steady at all RPM/load levels and it drives very well.
However, with the Mixer in place (fitted directly on top of the carb
the Petrol A/F ratio is fine at idle but drops off the bottom of the
gauge (dangerously lean) immediately over idle and becomes very
difficult to drive. Operating the manual choke about halfway restores
the petrol A/F to the optimum setting and full performance is
restored. The mixer is seriously interfering with the pressure /
airflow through the carb, but this must be a relatively standard set
up and I can’t believe this is considered acceptable (which is what my
kit supplier is suggesting). I am hoping you chaps might be able to
explain why / what I should do about it.

Van/Carb/LPG Mixer Details: Talbot Express 2.0 Litre, estimated
75bhp, Solex PBISA 34 fixed-Jet carb, Carb venturi diameter 25mm,
Mixer Venturi diameter 27mm (Autronic LPG kit with 2-stage Vaporiser
(not fitted yet))..

Thank you very much.
Steve

In article
, Max
wrote:
I have installed a lambda probe just below the exhaust manifold and a
dashboard Lambda gauge to instantaneously monitor Air/ Fuel (A/F) ratio.

Can't help directly with the Q but is your sensor a 'wide band' ?

--
Terminal_Crazy

Mitch - 1995 Z28 LT1 M6
Lancashire England http://www.sand-hill.freeserve.co.uk/terminal_crazy/

On 4 Jan, 10:55, Terminal Crazy Terminal_Cr...@sand-
hill.freeserve.co.uk wrote:
In article
, Max

wrote:
I have installed a lambda probe just below the exhaust manifold and a
dashboard Lambda gauge to instantaneously monitor Air/ Fuel (A/F) ratio.

Can't help directly with the Q but is your sensor a 'wide band' ?

--
Terminal_Crazy


No, narrow band 0-1v, but that has nothing to do with the physical
issue as the performance is vary apparent without the gauge (almost
undrivable until the choke is applied) and the sensor/gauge merely
identifies why. Half choke immediately brings the mixtures back to
where they are on petrol without the mixer fitted and it surges ahead
(!) exactly as it does without the mixer.
Regards, Steve

Nedavno Max napisa:

No, narrow band 0-1v, but that has nothing to do with the physical
issue as the performance is vary apparent without the gauge (almost
undrivable until the choke is applied) and the sensor/gauge merely
identifies why. Half choke immediately brings the mixtures back to
where they are on petrol without the mixer fitted and it surges ahead
(!) exactly as it does without the mixer.


Change the mixer? Perhaps you have wrong type mixer for your engine.


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/__/ / \ ** Registrovani korisnik Linuksa #291606 **
/ / \/ /\ \ ** Registered Linux user #291606 **
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On 4 Jan, 12:31, Yvan wrote:
Nedavno Max napisa:

No, narrow band 0-1v, but that has nothing to do with the physical
issue as the performance is vary apparent without the gauge (almost
undrivable until the choke is applied) and the sensor/gauge merely
identifies why. Half choke immediately brings the mixtures back to
where they are on petrol without the mixer fitted and it surges ahead
(!) exactly as it does without the mixer.

Change the mixer? Perhaps you have wrong type mixer for your engine.

*Registrovani korisnik Linuksa #291606 **


Thank you for the comment.

I am hoping it is an incorrect mixer however mixer venturi of 27mm
equates to the recommended 7.7mm2 per BHP and the kit supplier does
not seem to appreciate the severity of the problem. I am asking here
because it is my first LPG conversion and I'm hoing for experienced
installers' advice. I don't understand why the mixture is going weak
rather than rich, and I don't want to guess with a different Mixer
venturi size (0mm2 per BHP would equate to 31mm diameter) if it turns
out still to be incorrect, especially if I cannot get the kit supplier
to exchange the original.

Regards,
Steve

Nedavno Max napisa:

Thank you for the comment.

You are welcome.


I am hoping it is an incorrect mixer however mixer venturi of 27mm
equates to the recommended 7.7mm2 per BHP and the kit supplier does
not seem to appreciate the severity of the problem. I am asking here
because it is my first LPG conversion and I'm hoing for experienced
installers' advice. I don't understand why the mixture is going weak
rather than rich, and I don't want to guess with a different Mixer
venturi size (0mm2 per BHP would equate to 31mm diameter) if it turns
out still to be incorrect, especially if I cannot get the kit supplier
to exchange the original.


I am afraid that I can not help you much, I am no LPG expert, I just
had few problems with my carburetor, and picked up few things trying to
fix it.

Mixer with 27 mm venturi sounds OK to me for your engine (I have 75 BHP
1.6 liter BMW that had the same size venturi).

When I wrote that you may have the wrong mixer I thought about its
shape. Does it block some openings that carburetor needs for proper
operation? Look at the mixer I have:

http://www.ptt.yu/korisnici/i/v/ivic...MixerPlate.jpg

Notice two openings. Perhaps your mixer is not designed for your
carburetor. Try he

http://www.shopgas.de/

at the top left corner there is "Suchen". Type "Solex" and click OK.
You should now be able to see a list of mixers and (for most of them)
photos of mixers. See if yours looks like similar.

For more help try asking he


http://www.lpgforum.co.uk/




--
___ ____
/__/ / \ ** Registrovani korisnik Linuksa #291606 **
/ / \/ /\ \ ** Registered Linux user #291606 **
/__/\____/--\__\ ** http://counter.li.org/ **

On 4 Jan, 17:16, Yvan wrote:
Nedavno Max napisa:

Thank you for the comment.

You are welcome.

I am hoping it is an incorrect mixer however mixer venturi of 27mm
equates to the recommended 7.7mm2 per BHP and the kit supplier does
not seem to appreciate the severity of the problem. I am asking here
because it is my first LPG conversion and I'm hoing for experienced
installers' advice. I don't understand why the mixture is going weak
rather than rich, and I don't want to guess with a different Mixer
venturi size (0mm2 per BHP would equate to 31mm diameter) if it turns
out still to be incorrect, especially if I cannot get the kit supplier
to exchange the original.

I am afraid that I can not help you much, I am no LPG expert, I just
had few problems with my carburetor, and picked up few things trying to
fix it.

Mixer with 27 mm venturi sounds OK to me for your engine (I have 75 BHP
1.6 liter BMW that had the same size venturi).

When I wrote that you may have the wrong mixer I thought about its
shape. Does it block some openings that carburetor needs for proper
operation? Look at the mixer I have:

http://www.ptt.yu/korisnici/i/v/ivic...MixerPlate.jpg

Notice two openings. Perhaps your mixer is not designed for your
carburetor. Try he

http://www.shopgas.de/

at the top left corner there is "Suchen". Type "Solex" and click OK.
You should now be able to see a list of mixers and (for most of them)
photos of mixers. See if yours looks like similar.

For more help try asking he

http://www.lpgforum.co.uk/

--
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/__/ / \ ** Registrovani korisnik Linuksa #291606 **
/ / \/ /\ \ ** Registered Linux user #291606 **
/__/\____/--\__\ **http://counter.li.org/**

Hello again.

Cracked it! I discovered this evening that I need to move the mixer
further from the carb. I moved it upstream 10cm on a mount made from a
lemonade bottle (picture here http://www.pw5100.fsnet.co.uk/autosl...iser_Small.jpg
). It worked a treat. The Original location was causing a vacuum /
vortex directly over the air intake to the float chamber and at least
one jet.

It now runs slightly rich at all times (12.5 as one would expect due
to the slight constriction caused by the mixer) which is superb. I'm
sending the original back to the supplier tomorrow asking for a
replacement that fits in the hose to the airfilter. It will be
upstream of the crank emission intake though to I'm going to have to
move that or LPG will be sucked into the crank!

No worries. Thank you for your help, and to the others that took the
time to reply.

Best wishes,
Steve

Nedavno Max napisa:

The Original location was causing a vacuum / vortex directly over the
air intake to the float chamber and at least one jet.

That's what I was thinking of when I wrote "wrong type mixer for your
engine". But since English is not my native language...

Anyway, I am glad that you found the solution.



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___ ____
/__/ / \ ** Registrovani korisnik Linuksa #291606 **
/ / \/ /\ \ ** Registered Linux user #291606 **
/__/\____/--\__\ ** http://counter.li.org/ **