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 Weak mixture on one bank, Weber 32/36 DGV
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andydeans3
V4 Guru

United Kingdom
1579 Posts

Posted - 07 Aug 2021 :  18:07:25 Show Profile Reply with Quote
The carb is a 32/36 Twin choke Weber DGV. Brand new about 6 years ago.

Historically the mixture always seemed correct, nice sandy brown coloured plugs.
Then as part of a fault finding exercise I replaced the mechanical fuel pump, with an electric pump, meant for an MGB.
It was about then I noticed that the plugs were nearly white.
I also refitted the mechanical pump, and now have the electric pump, feeding the mechanical pump.

I have been in touch with Fast Road cars who suggested I up the idle jets from 55/50, to 60/55.
This I have done.
The pair of plugs below are one from the left bank, (white),and one from the right bank, (reasonable sandy brown colour).
The single plug is from the left bank. I didn't take out the front right hand plug because of the hassle with the alternator in the way!
The plug colours you see are AFTER upping the idle jets.

Does anyone have any other ideas? Especially, why is one bank weak, and one bank seem about right.





1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro

SAAB96L
V4 Fan

United Kingdom
147 Posts

Posted - 07 Aug 2021 :  19:49:33 Show Profile Reply with Quote
Hello Andy,

Firstly what was your fault finding exercise ??

The left bank is certainly running lean - more so on one cylinder than the other (single plug) whilst the other left bank plug is between that sandy colour and the extreme white.

If the carb has been okay for the last six years and the lean running has only just occurred, then it is likely that either the carb has gone out of balance or there is an air leak on the left bank.

Anthony Boshir-Jones of FRC certainly knows his stuff, but I'm not sure how upping the idle jets will resolve the issue; which it has not. If anything, this whitening is a result of the engine being driven for a length of time, causing the plug(s) to go white.

Doubt the issue is timing, but as mentioned either the carb is functioning incorrectly (non-balanced fuel delivery) or the ingress of additional air in to the left bank causing the imbalance.

I take it, the car runs okay with any hesitation or signs of misfire ??

Additionally, how old are the plugs and I assume they are BP6ES ??

Regards.

Richard.





Edited by - SAAB96L on 07 Aug 2021 19:52:31
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christophe
V4 Fan

France
127 Posts

Posted - 07 Aug 2021 :  21:29:05 Show Profile Reply with Quote
I found almost the same condition (less pronouced) on my car a few days ago. I run a 1,7l engine coming from a Transit with a Fomoco carb. So, I would say your carb is not the culprit, especially if it is only 6 years old. I found that the exhaust valves were too tight on a bank of cylinders, but I do not know for sure if the problem came from here yet. In such cases, I usually hook a vacuum gauge on the intake manifold and set the mixture to get the higher value.
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andydeans3
V4 Guru

United Kingdom
1579 Posts

Posted - 08 Aug 2021 :  12:41:57 Show Profile Reply with Quote
quote:
Originally posted by SAAB96L
Hello Andy,

Firstly what was your fault finding exercise ??

The left bank is certainly running lean - more so on one cylinder than the other (single plug) whilst the other left bank plug is between that sandy colour and the extreme white.

If the carb has been okay for the last six years and the lean running has only just occurred, then it is likely that either the carb has gone out of balance or there is an air leak on the left bank.

Anthony Boshir-Jones of FRC certainly knows his stuff, but I'm not sure how upping the idle jets will resolve the issue; which it has not. If anything, this whitening is a result of the engine being driven for a length of time, causing the plug(s) to go white.

Doubt the issue is timing, but as mentioned either the carb is functioning incorrectly (non-balanced fuel delivery) or the ingress of additional air in to the left bank causing the imbalance.

I take it, the car runs okay with any hesitation or signs of misfire ??

Additionally, how old are the plugs and I assume they are BP6ES ??

Regards.

Richard.


How much time have you got?
The fault finding exercise pertained to a long standing issue that have had with the car.
This only happened, VERY occasionally, 3 or 4 times a year perhaps.
It would suddenly just stop. At the outset, I'd look under the bonnet, look for obvious disconnected wires etc.
Then I noticed that the fuel filter bowl was completely empty. Turn the car over, off she would go.
It got to the point, 2 or 3 years down the line when I wouldn't even bother lifting the bonnet. Just wait 30 seconds, off she would go.
I spoke to Steve at Malbrad at some point, and he suggested putting a check valve under the back seat. There already was one just below the crab fuel inlet.
I did this, and the problem vanished.....for a couple of years. It then came back last year. I had already renewed the fuel pump at some point. Since I had a new MGB electric fuel pump, still in its box, I decided to try that. It was around this time that I noticed that the car was running weak. One suggestion from the forum was that the MGB fuel pump, does not put out the same pressure as the mechanical pump. I then decide to try the MGB pump, feeding the mechanical pump, which is where we are today.
One suggestion that's come up more recently for the cutting out issues, is fuel vaporisation. This would fit with the fact that the issue simply disappears once the engine has stopped for a few minutes.

The cutting out problem has vanished, but I'm left with this weird left bank running weak.
The fuel pump set up may have nothing to do with this of course.

Christophe. I will check the tappets, though they were done, not that long ago.

-----UPDATE-----
Since writing the above this morning, I've removed the carb, checked the fuel bowl, all the jets etc, and renewed all the gaskets between the manifold, the plate and spacer, and the carb.
Running it now, and spraying WD 40 all round the bottom of the carb, and the various connections, it seems to be sealed. I should have tried the "ol' WD40 trick", before taking it all apart of course.....

Andy

1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro

Edited by - andydeans3 on 08 Aug 2021 15:15:22
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Derek
V4 Guru

United Kingdom
2050 Posts

Posted - 08 Aug 2021 :  17:34:38 Show Profile Reply with Quote
The 32/36 isn't a dual choke carb as both the 32 and the 36 feed all cylinders. That means that any given throttle opening the mixture is feeding the manifold. You could have an air leak on that side (manifold to head gasket, check manifold nuts/bolts) if the weak plugs are both from the same head. From your post that seems to be the case but I'd persevere and get the awkward plug out. Your Saab tool kit appears to be missing the short spanner with the stubby lever welded to it? I think it's also possible to have an exhaust leak cause this condition?

Edited by - Derek on 08 Aug 2021 17:40:12
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andydeans3
V4 Guru

United Kingdom
1579 Posts

Posted - 08 Aug 2021 :  21:36:44 Show Profile Reply with Quote
Derek
I wasn't aware of the strict twin choke definition.
Always thought of it as a twin choke carb.
Anyway.....
I use a ring spanner to get that number 1 plug out, it's just a hassle.
I will take it out the morn.
I've checked around the carb to manifold connections with WD 40, perhaps need to move down to the inlet manifold gasket.
I'm thinking the inlet manifold perhaps needs to come off, I've got a new gasket.....

1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro

Edited by - andydeans3 on 09 Aug 2021 10:08:21
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Derek
V4 Guru

United Kingdom
2050 Posts

Posted - 09 Aug 2021 :  11:38:49 Show Profile Reply with Quote
It is a twin choke but is progressive so the first "economy" choke opens fist and then the second "performance choke opens when you want more go. That way the gas speed in the first choke can be high fo efficiency.

Model Number Common Name Notes
32/36 DGV (5A) DGV Progressive throttles, Manual choke
(standard for Formula Ford 1600, Formula Ford 2000, and Sports 2000)
32/36 DGAV DGV Automatic choke (A = Aqua; water-operated)
32/36 DGEV DGV Automatic choke (E = Electrically-operated)
32/36 DFAV, 32/36 DFEV DFV Should be a mirror-image of DGV series,
but only the jets interchange!*
38/38 DGAS, 38/38 DGES DGAS Synchronous throttles, otherwise a DGV

40 DCOE, 45 DCOE, 48 DCO, 50 DCO, 55 DCOE DCOE Dual-throat side draft. E used to indicate a trapezoidal mount. The E has largely been dropped but the trapezoid remains.
46 IDA, 48 IDA IDA (dual) Dual-throat downdraft
40 IDA 3, 46 IDA 3 IDA (triple) 3-throat downdraft specifically for Porsche flat-6
(nothing interchanges with IDA dual!)
40 IDF, 44 IDF IDF Dual-throat downdraft
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melle
V4 Guru

United Kingdom
3418 Posts

Posted - 09 Aug 2021 :  20:36:20 Show Profile Reply with Quote
Check if the intake manifold bolts are tight, they have a tendency of coming loose over time. If you/ someone else has used an intake gasket from a cheap set it may be worth replacing it with a better one, some are exceptionally poorly made.

www.saabv4.com
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andydeans3
V4 Guru

United Kingdom
1579 Posts

Posted - 09 Aug 2021 :  22:40:11 Show Profile Reply with Quote
Aye, Melle, the bolts are not slack so changing the gasket was my next port of call.

The gasket in the car now, and the spare inlet manifold gasket that I have, were bought from Malbrad, so I'd hope their good quality.
I'm busy doing other things this week, so hope to get back to it next week.
I'm going to Corbridge (Northumberland), Classic show on Sunday 15th August, so also don't want to start fiddling with the car before the show, anyway.
ps was hoping to see you at SAAB Fest this weekend past.

Andy

1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro

Edited by - andydeans3 on 09 Aug 2021 23:23:24
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andydeans3
V4 Guru

United Kingdom
1579 Posts

Posted - 10 Aug 2021 :  12:11:13 Show Profile Reply with Quote
Here are all 4 plugs, 1 and 2 at the top. 3 and 4 at the bottom.
Number 3 seems much whiter than the other 3.

I have tried spraying WCP all around the inlet manifold, to see if it gives any indication of air being drawn, but that drew a blank.
Same around the carburettor flanges and various connections in the area. Nothing.



1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro

Edited by - andydeans3 on 10 Aug 2021 12:13:43
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SAAB96L
V4 Fan

United Kingdom
147 Posts

Posted - 10 Aug 2021 :  14:13:29 Show Profile Reply with Quote
Andy,

Could this be as simple as, a faulty spark plug where its heat range resilience is starting to degrade ??

My experience of spark plugs where the insulator goes white is:

Ignition too far advanced / lean fuel mixture / cooling issue within the combustion chamber chamber which is often caused by excessive combustion deposits.

Spark plug insulators start to go white, when the combustion chamber reaches temperatures in excess of about 850 degrees C for a prolonged period of time. The optimum operating range is between 450 C and 850 C. As you can see, the examples I mentioned earlier will certainly raise the combustion chamber operating temperature.

However, over a period of time I would expect all the plugs to be white if one of the above was applicable - hence my opening line concerning a single defective plug.

If you have a digital laser thermometer, that would certainly be a useful test to ascertain that the plugs and the immediate surrounding area of the cylinder head reads the same within reason.

You didn't confirm if you are using BP6ES plugs and I cannot make that out from the previous photos.

Just a few ideas.

Regards.

Richard.

Edited by - SAAB96L on 10 Aug 2021 14:14:54
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andydeans3
V4 Guru

United Kingdom
1579 Posts

Posted - 24 Aug 2021 :  13:15:10 Show Profile Reply with Quote
I've come back to look at this issue again.
I can confirm that the plugs are NGK BP6ES, bought from Malbrad.

I have now removed the inlet manifold, to change the inlet manifold gasket. I can see no evidence of any air leaks around cylinder number 3, or anywhere else for that matter.

One question I wanted ask the "assembled".
Why are there 2 blocked off waterways at the front of the engine. Just a small pin hole to balance the water pressure I suppose.
You can see them at the left hand end of the photo below. The new gasket. The old gasket is identical. Just morbid curiosity.

The lower photos show the manifold after I removed the old gasket.
It came off quite cleanly, just leaving a bit of residue round the water ports.

Since I found no clear evidence of an air leak, I don't think I've solved this issue...............Perhaps a very, very small air leak, that's left no trace?
We'll see what happens when I get it all back together again, and running.



Before Cleaning up faces


After cleaning up faces



I used a hoover to prevent dust/crud falling into the engine ports, while removing old gasket material.





1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro

Edited by - andydeans3 on 24 Aug 2021 13:20:49
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melle
V4 Guru

United Kingdom
3418 Posts

Posted - 24 Aug 2021 :  16:49:42 Show Profile Reply with Quote
The small holes are air bleeds.

www.saabv4.com
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Woody
V4 Guru

United Kingdom
2549 Posts

Posted - 26 Aug 2021 :  15:02:49 Show Profile Reply with Quote
The air bleed parts of inlet manifold used to have copper plates in the original Saab gaskets.
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andydeans3
V4 Guru

United Kingdom
1579 Posts

Posted - 14 Sep 2021 :  01:05:42 Show Profile Reply with Quote
I'm having a fuel starvation saga, it's across on the UKSAABS site.
I had all the plugs out on Thursday, on my way down to Stratford.

Well, plug number 3 is still white as a ghost......
Any more ideas as to how I can be drawing extra air, into one cylinder only?

1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro

Edited by - andydeans3 on 14 Sep 2021 01:07:06
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melle
V4 Guru

United Kingdom
3418 Posts

Posted - 14 Sep 2021 :  07:53:33 Show Profile Reply with Quote
Really difficult to diagnose something like this from a distance, so I can only shoot ideas from the hip really. Does the no. 3 plug seat OK, and is there no damage to the threads or the seat in the head? HG leak, i.e., coolant leak to no. 3 cylinder? How's the coolant level and ave you recently done a compression test? When did you last adjust the valves? Does the thermostat open at all?

www.saabv4.com
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