Series 3 2+2 1972 - Ignition Issues

[chris420sa]

My Series 3 is fitted with the SNGB electronic ignition replacement (DAB113HE) although I do not have the records to know when it was fitted by a PO.

I fairly recently fitted a vacuum advance with vacuum source from rear side of rear lh inlet manifold and timing was re-set to suit. Original vacuum retard vacuum source on rear lh carb was plugged.

Having rebuilt the 4 carbs, I started the engine and took the car for a run. It misfired quite a bit and lacked power. Subseqent attempts to start the engine have failed.

I removed the spark plugs to examine – they were wet and black (although the carbs had been set up reasonably lean).

The problem definitely seemed to me to be on the ignition side so I did the following:

1. Checked the incoming voltage from the ignition switch (white wire) to the “ballast resistor” – at least 12 volts recorded
2. Changed the ignition coil for a new one from SNGB just in case
3. Checked that at least 12 volts was present from +ve terminal of the coil to earth and then from -ve terminal to earth – all fine
4. The plug leads and coil to distributor lead are reasonably new (set purchased from SNGB) as are the spark plugs
5. I fitted a new distributor cap after checking that the rotor was OK and cleaning up the contact surfaces
6. Not sure if the plastic "spark shield" plays any role/has a required orientation?
7. I removed the “amplifier” and replaced the “GM 4 prong ignition module” with a new one including thermal conductivity “paste” on underside
8. I checked for continuity between the wiring on terminals G and W of the above module and the plug to the distributor – all fine
9. I checked for continuity between the wiring on terminals B and C of the above module and the connector block which goes to the other side of the “ballast resistor” – all fine
10. The amplifier unit is well earthed (grounded) via its mountings to the block- I checked the earthing.
11. Reconnected all, removed spark plug from 6B, cranked engine. The resulting spark was weak (orange colour) and less frequent than it should be.
12. Ditto 11 above with the plug from 6A
13. Needless to say the engine would not start with chokes almost fully on
14. I did notice that the +ve and -ve leads from the battery were quite hot after the cranking.
I understand (?) that the ignition system no longer uses a “starting boost” from the starter/ballast resistor relay.
The only part of the circuit which I have not examined (as I'm not sure what I should be looking for) is the pick-up etc in the distributor.
I have looked at the installation guide for the electronic ignition replacement (there's one on the Limora site) but it does not help with fault-finding.
Greatly appreciate if a member who has had similar problems could advise re fault-finding/testing.
I live in Ditchling (BN6 - East Sussex), so if a member knows of a reasonably local expert, that could also be helpful.
All the best
Chris

[tonyabacus]

Chris

Can we get a couple of answers first,
1. How did the car start and run before you did any of this work
2. Had the car been left standing for any length of time before doing this work.
3. Why did you need to fit the new vacuum advance?
4. When you started the car after fitting the vacuum advance, did the car tick over as normal
5. It seems you have fitted a number of new items, plugs, leads and other parts, but were these fitted after the poor test run, or were some of these already installed before the change of vacuum advance.
6. The carb rebuild, did you do a full replacement of all the seals, washers and diaphragms etc

Perhaps also if possible can you take a picture of where you have made the new vacuum advance take off point and post it for us to see.

Tony

[lowact]

I would not dismiss the possibility that the problem is on the fuel side. If it’s too rich it won’t ignite, even with good spark. Are you saying it was ok before you rebuilt the carbs?

The flash shield protects the electronics (pick-up from any stray HT arching. Also it should have an embossed radial line, should be pointing at the left headlight, is TDC, i.e. when the timing mark on the front crankshaft damper is lined up with 0 deg. BTDC the distributor rotor should be pointing exactly along the radial line embossed into the flash shield. At very least this would indicate the distributor is in the correct OEM position – there are 14 teeth on the distributor drive gear, so if it is one tooth out the rotor button would miss the flash shield radial line by 360/14 = 26 degrees.

SNGB sell two ignition kits: DAB113HE and DAB113HEF (F on the end) One has a vacuum retard distributor, the other has a vacuum advance distributor. Read all about it here …
viewtopic.php?f=6&t=15092

I don’t know if you can change an SNGB vacuum retard distributor to a vacuum advance distributor just by swapping the vacuum modules? If you have a working vacuum advance, when you suck on the distributor vacuum module, the distributor mechanism (incl. reluctor pick-up) should move clockwise and hold until you remove the suction. Not having vacuum advance would not be stopping yr car from starting however.

Car should start easily with timing anywhere between 8 deg BTDC to 4 deg. ATDC. If you’ve got a spark, even a weak one, unless yr timings out by miles, its more likely carb's, even just the choke?

[chris420sa]

Tony and Colin - many thanks for your responses.
To answer Tony's questions first:

1. How did the car start and run before you did any of this work It started reasonably well although slightly reluctant and ran OK but there was a flat spot which prompted me to do the rebuild of the carbs
2. Had the car been left standing for any length of time before doing this work. No
3. Why did you need to fit the new vacuum advance? I'd disconnected the vacuum retard and plugged the lh rear carb vacuum port some time ago and decided to instal the vacuum advance unit - that was done well before the problems arose. Vacuum advance is connected to a port on the rear of the rear inlet manifold just above the reservac braking tank vacuum take off
4. When you started the car after fitting the vacuum advance, did the car tick over as normal Yes, no problems- timing was reset by strobe
5. It seems you have fitted a number of new items, plugs, leads and other parts, but were these fitted after the poor test run, or were some of these already installed before the change of vacuum advance.Plug leads were fitted about one year ago, ignition coil and dissie cap and 4 prong module in the amplifier were replaced last week after the problems arose
6. The carb rebuild, did you do a full replacement of all the seals, washers and diaphragms etcYes except the diaphragms which I checked and found to be fine. I also adjusted the temp compensators to open and close at the correct temps and I blanked off the by-pass valves. Also checked the chokes and fitted new gaskets

Perhaps also if possible can you take a picture of where you have made the new vacuum advance take off point and post it for us to see. Please see my response under item 3 above

Turning to Colin's responses:

The sparks are weak and seem to be too sporadic but were OK before my testoterone level rose and I rebuilt the carbs
I'll check the flash shield for the embossed radial line - thanks for that advice
My replacement ignition kit is identified on the amplifier casing as DAB113HE.
It was not much of a problem to fit the vacuum advance diaphragm to the dissie.
I checked the movement of the pick-up by sucking on the vacuum pipe - moved OK cwse

Guys, I hope my responses to your questions have helped and look forward to hearing from you.
It's raining in the UK today so no problem to lock myself in the man shed for as long as it takes!
Best regards
Chris

[jagwit]

Having rebuilt the 4 carbs,

Chris, I'm with Colin on this one. I too place more suspicion on the carbs than I do on the ignition system.

If there is one thing I learnt in my automotive adventures, it is how quickly a plug fouls when being overfuelled. You are stating that you rebuilt the carbs. That implies that you have tuned them CORRECTLY. But then....

I removed the spark plugs to examine – they were wet and black

A wet spark plug does is not good and confirms overfuelling. A black spark plug is even worse. A wet black spark plug is as bad as it gets.

A wet plug is easy to explain: WAAAAYYYY to much fuel during cranking. This could result not only from the enrichment valve (choke) not working correctly (supplying too much fuel) but also from the main jet not being set correctly (too much fuel) as well as the float levels not being correct (too high - also leading to overfuelling - the latter easy to see).

A set of black spark plugs should immediately be replaced with good clean ones (or be media blasted clean again) even if just for diagnosing. It is too easy for the spark to be shorted out to the body via the black carbon that has been deposited on the body and could easily result in what appears to be a weak spark or none at all - when in fact there IS a spark, except one can not see it because the spark plug is fouled so much that the spark current is just being routed through the carbon layer on the spark plug.

I was once called to a Land Rover Discovery 1 with the 3.9L EFI V8 engine that would not start. I checked the basics and replaced the plugs with new (The plugs that came out were very black). It started instantly. Owner protested "but those WERE new plugs in there!!" BUT blackish smoke was coming out the tail pipe confirming overfuelling. Installed my spare good MAF and voila!! Happy engine. The point is: those new plugs the owner installed were fouled within minutes of running overly rich.

Chris, with everything you have done on ignition, I agree with Colin that its rather unlikely that your problem is ignition related. I would re-visit the carbs first. Rather set those mains needles on the leanish side than on the rich side and re-check that the enrichment valves are NOT engaged when choke = off, and installed and set correctly.

[jagwit]

13. Needless to say the engine would not start with chokes almost fully on

If I apply too much choke on my car, I get no sign of life. In fact, I've come to regard the "choke" as extremely "aggressive". Most of the time, pulling choke to the first detent, is more than enough, still requiring pushing it some way back immediately after the start.

So, I'm saying that those "chokes almost fully on" may in fact be the reason for the wet plugs and a no start.

[Whitact]

Just a thought: one thing that is very easily done when rebuilding these carbs is to fit the "choke" discs the wrong way round which will obviously result in a very rich mixture at all times. The diagrams in the manuals are none to clear and easy to misinterpret. Might be worth double checking.
Cheers

[chrisfell]

Dunno about the rest of you, but when I’ve done something to the car and the next drive or the test drive shows up some flaws, I know absolutely without fail, it was the thing I just did.

[tonyabacus]

Chris

Thanks for the responses to my questions. I think that perhaps the point that strikes me immediately is that whilst a reluctant starter before your current troubles, the car sounded as if it did start and ran reasonably okay. I think like Colin and others that this possibly points more towards the fuelling side than the ignition side. There is perhaps more likely to be an issue with the rebuilding of the carbs as others have mentioned and certainly I would be looking also at putting in new diaphragms, over a number of years these tend to become a little distorted and can cause issues.

However, when chasing problems like this it is too easy to get diverted, so the starting point for me is to go back and strip and rebuild the carbs again, paying particular attention to getting every setting correct. I know its a pain but at least then you will be certain that they have been put back together as per the book.

For me also the fact that the plugs were wet and black points towards the choke side of things, depending on ambient temperatures and how cold the engine has become may distract owners into using too much choke. The weather in the UK over the past few weeks has not been cold enough to warrant much choke at all. As one of the guys has mentioned he finds the choke to aggressive and I would suggest using hardly any choke when you try to start next time.

Once you get it running take it for a drive and then kill the engine as soon as you stop back home. Don't let it idle, pull out a couple of plugs and look at the colour, if they are still black (they should be dry) then its pointing towards either the choke mechanism sticking/faulty or the mixture now requires fine tuning. Once warm and if the plugs are still black, I would disconnect the choke mechanism, clean the plugs as best as you can and take it for another run, if on return the plugs are black once more then at least you know it is not the choke and you can direct efforts at the mixture adjustment.

Forgot to ask previously, but have assumed that the air filter and pathways to the carbs are all good?
Tony

[chris420sa]

Philip, Adrian, Tony - many thanks for your very helpful responses.

Could well be a fuel issue.

I replaced the plugs with a cleaner set and also checked the plug leads - the resistances of the "silicon" leads (as supplied by SNGB a year or so ago) were quite variable in terms of "ohms per inch length" , which surprised me. I only tested the "A" bank. The results were:
1A: 800; 2A:1000; 3A:890; 4A:853; 5A:1055; 6A:861 and the coil to dissie lead: 643
All varied a bit when I bent them a bit to check for obvious poor continuity.

Tried to start her but she only fired a bit and at very slow revs with the choke just on.

Looks like I'll have to take the carbs off again and check everything, but...
I've added a photo of the LH choke disc taken before I reinstalled it. If poss, could you please advise if you think the "orientation" is correct.
My logic was that the fuel slot in the disc in choke off position is cwse of the fuel to choke supply orifice when viewed from the disc side such that when the choke is operated, the slot is rotated cwse when viewed looking towards the side of the carb (which would be anti-cwse if viewed from the disc side) in order to be positioned over the fuel supply and thus provide fuel to the inlet via the two sets of 4 holes.


Look forward to your further thoughts on this.
Best regards
Chris

[tonyabacus]

Chris
Not sure if this will be of help, its a dealer training document for Strombergs on a Triumph, but the principle of setting up the choke should be the same,

https://www.triumphwedgeowners.org/uplo ... mplete.pdf

Also not a big fan of carbon leads for the reasons you have found, so perhaps once you are up and running, maybe a change over to some good wire cores.

Rather hurried response as I am dashing away for a week, but will check back on return, hope you are sorted by then

Tony

[jagwit]

I only tested the "A" bank. The results were:
1A: 800; 2A:1000; 3A:890; 4A:853; 5A:1055; 6A:861 and the coil to dissie lead: 643
All varied a bit when I bent them a bit to check for obvious poor continuity.

Nothing wrong there. Those kinds of variation is nothing alarming.

I do NOT recommend copper core wire. It will generate masses of electromagnetic noise and everybody listening to a radio around you will be cursing you for polluting the air waves.

[chris420sa]

Tony and Phillip - many thanks for your responses.

Phillip - did you get a chance to look at the photo of my choke and advise your thoughts on the correct orientation when re-assembling?

Best regards

Chris

[jagwit]

I did Chris, but without stripping a carb known to be correct, or having a carb I can study in detail, I can not confidently make recommendations. Sorry mate.

I would want to know where the fuel is coming from when enrichment is called for, and where it is going. Obviously, the disk must be positioned and oriented such that when it is rotated (as it would be when choke is activated ), the smallest of those orifices come into play first, adding them progressively as more enrichment is applied.

[baganz.sven@web.de]

Hi,

from my point of view the orientation looks good. At least it is the same like my carbs have.
But the holes look quite big. ?
Sven

[MarkRado]

Chris,
judging from the photos from the discs, someone seems to have drilled yours in the past- maybe in an attempt to help starting. I'd go for new discs.