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MG MGB Technical - Lean vs Rich plug appearance

Mk 1 B, 3 brg, original HS4 SU's, etc...

Having trouble starting after a few weeks non use in cold weather. Then it would always flood trying to start, then ran OK once started.

A friend lightened the dashpot oil (replaced 20w50 with light "sewing machine" oil) and raised the jets (ie leaner) On uphill runs in top gear the engine misses and splutters but runs smoothly on the flat or downhill. The plugs seem to indicate lean (rear two) and rich (front two). Do you agree?
Given the jets are already set higher than they were, I'm puzzled why the front plugs are black.

I don't know what size needles/jets I have (installed by PO) should I start over with new known needles/jets and retune as per manual?
I have just fitted NGK plugs as my friend looked most displeased when he saw the Delco plugs I had.

Here are the front plugs.


John Minchin

....and here are the rear two.


John Minchin

John,
How many miles have you done on these plugs?
It also looks like some small metallic deposits on them especially the lean ones!
Personally I would go back to 20W50 and start the set-up from scratch as per the book eg timing, valves and then carbs... but it won't hurt to at least check the jets, needles and float setting.

Best of....
MGmike
M McAndrew

Mike
Very little mileage - couple of hundred max
prior to the recent adjustments I hadn't noticed these particles before.
I'd better check oil and filter to see if any particles there. :-(

John
John Minchin

I would be worried that it could be too lean and burning the piston top (metal particles). That said plug colour doesnt look too lean from photo.
Mike
Mike Ellsmore

I'm with Mike E- looks a bit like it could get nasty if left like that
I'd be taking it to some one that has experience with su carbs etc there are plenty down your way
You are in Hobart if I remember correctly--
May I suggest Shorty

Your hard starting and missfire problem has all the symptoms of dead fuel
Don't forget the fuel around here is crap if you are leaving your car sitting around unused a bit.
I'd be making sure you have premium in it when left sitting

cheers willy
William Revit

If the needles are worn at the idle position (thickest & most likely wear point) then a higher jet setting which makes the mixture right there will be lean elsewhere. BTW unleaded fuel will always give black plugs, it's the different shades of black that you need to interpret.

However, I suspect the plugs are the wrong heat range. The rear two plugs look scroched, and althopugh very lean mixture might do this by far the most common cause is wrong heat range. Furthermore, misfiring under prolonged load (as in uphill) is another sign of plugs too hot in heat range, particularly if the misfiring doesn't start immediately the load comes on. Once the plugs are looking like 3&4, they will not come right and need to be replaced.

Over here, one of the retail chains Repco or Supercheap, not sure which (or both) have a wrong supercession for spark plugs and supply BP5ES for the MGB which is definitely too hot running and always ends up looking like those 3&4 plugs. We see quite a lot come in like that. BP6ES is the correct heat range in NGK.
Paul Walbran

John,
there are lots of "light sewing machine" oils some thinner than others, it could be well under 15 or even 10 (engine oil)

I'd suggest you go back to 20w50 or better still, as I do, as recommended by John Twist and using 90 weight gear oil (no it's not too thick, it's between 40-60 engine oil)

NGK are normally the recommended plug to use and as Paul has put BP6ES

I too would go back to checking in this order - tappets, CB points, plugs gap/clean (replace?) and last carb mixture

I'd also check that no one has got the dashpot pistons and covers mixed up, see - 41 Matching SU Air Pistons - http://www.youtube.com/watch?v=IfU47Oqq9wA



Nigel Atkins

Lean is relative on those pics. The first two plugs look way over rich, especially the left one. Even the other two look rich to me for plugs taken out after, say, a five mile run at normal temperature. That speckling around the centre electrodes is also concerning. What are NGK they?

If the mixture is rich, then pulling the choke will make it richer than it would normally be on choke, which increases the risk of flooding at a cold start, especially with HSs, and especially if there is anything wrong with the state of tune.

At the very least, the carbs are significantly out of balance, you need to set them up for air flow and mixture balance from the very beginning. But before you can do that make sure everything else i.e. rockers and ignition is right first.

Missing or spluttering under load can indicate HT breakdown somewhere, the higher cylinder pressures make it harder for the plug to jump the gap, so the HT voltage rises, and will find any weak spots.

Dashpot oil will have very little effect on starting problems, lack of damping will show itself when opening the throttle to accelerate as a stumbling before it picks up.
Paul Hunt

One question.

How do you 'flood' an engine when you have carbs without an accelerator pump?
Bill Spohn

Bill, by having the choke out too far for the engine & ambient temperature conditions (extreme example: using full choke on a fully warmed up engine) or by cranking the engine too long on full choke when it isn't firing (for whatever reason) which is very effective in thoroughly wetting the plugs with fuel.
Paul Walbran

Thanks for all the comments/suggestions.

Clarifications - the plugs are AC Delco - I was told to change to NGK BP6ES and that's what I was doing when I found the plugs like this.

I've done only a couple of small trips since the recent adjustments - prior to that idling and running was fine and the only issue was starting on a cold day after a few weeks layoff .( then getting flooding and plug wetting as described, by repeated cranking)

The carb dashpot covers and pistons are matched and haven't been mixed up.
Fuel is 95 Octane unleaded.
BTW the change in dashpot oil was a side issue - I have some gear oil so will change to that.
The speckled "particles have not been seen before - I will need to find out what they are.

Carb balance I agree seems to be an issue. Ignition seems OK - reasonable spark (old plugs), dwell angle OK, dynamic timing perhaps slightly retarded (I was about to do some driving tests and advance it a bit. Points are as new.....

I think I will reset the carbs with new jets/needles and follow the accepted practice as detailed on this site to get them balanced and adjusted. But particles need checking first...
I'll keep you posted
John
John Minchin

John
As you are using 95 oct the fuel in itself shouldn't be the issue unless it's ethanol added stuff
you need to stick to known good brands like BP Shell etc
I think you are on the right track getting a new pair of needles and jets As Paul W suggests the mixture can be way out up higher in the revs if the idle mixture has been adjusted with worn needles/jets and having the timing retarded isn't going to help cold starting either It needs to be right on the mark at idle , setting it on the road can diguise other faults like seized advance or broken dist. springs
It needs to be set static and then the advance systems checked against a timing light to make sure all is as it should be
Also you need to have a good look at your choke linkages after the idle mixture/speed has been set up. As the choke is pulling on both choke speed ramps should operate equally and they need to pull both choke tubes equally as well (both adjustable)
It should start cold when all set up properly but if I could suggest a good external ballast resistor ignition coil would make a BIG difference to cold starting if the concours/purist thing isn't an issue
Also there are some really crappy ign points around here at the moment , they seem to be just plated instead of having good solid posts I've been sticking to the Bosch ones - they're good
The symptoms of the crap points are stumbly idle and unsmooth acceleration and feel a bit like a half dead sparkplug and flicky tacho
cheers willy
William Revit

Willy's post reminds me that there are also issues with some new rotor arms, particularly black ones with a rivetted contact. Get a good red one from Distributor Doctor, and get a set of his points too. Most supposedly carb problems are in fact caused by the distributor.
Mike Howlett

"a good external ballast resistor ignition coil would make a BIG difference to cold starting"

This would need a ballast resistance and a rubber bumper starter motor to be of any benefit.

If you just fit the rubber bumper coil without the ballast resistance that was standard on those cars you will overheat the coil and burn the points as you will be running with double the coil current.

Even if you fit the external ballast with the later coil - which is designed to give a boost to the spark while cranking, unless you fit the later starter motor as well, or a relay or diode system to bypass the ballast resistance during cranking, you will not get the boosted HT and the spark will be exactly the same as with the original coil.
Paul Hunt

Paul,

I haven't looked at the RB wiring diagram as of yet, therefore (for the benefit of all) could you explain the requirement for a RB starter motor?

A simple wire from the starter solenoid to the coil +ve will provide the required 12v boost during cranking and the existing coil supply connects to the ballast resistor to provide the running supply (this assumes the solenoid cable is sufficient to carry the current requirement of both).

Ahh, I've just spotted the problem with the above! It would result in the solenoid having a permanent 6v supply in running mode! A blocking diode or relay would be required. I guess this is built in to the later starter motor?

best of....
MGmike
M McAndrew

The 2M100 starter was fitted from 1971 right through to the end of production so any of those cars will have the back contact needed to bypass the ballast, though obviously it wasn't wired up until the 77 model year when the ballast was introduced.

However, there are other ways of achieving the same result (for example a relay in parallel, activated by the white/red wire), and so long as the wiring is arranged so that ballast is bypassed while the starter is in operation then the benefit of a ballast resistor will be gained.

An externally ballasted coil is certainly one of the best retro-fits for reliable cold starting, and a cheap one at that.

Good that the plugs are BP6ES, but I'd still be concerned about that scorched look on the 3&4 plugs as it's not healthy for an engine. It may be mixture related, but occasionally an engine (for a variety of reasons) needs a colder running plug. What heat range were the AC Delcos? If they are a direct cross reference from BP6ES and were running normally then that definitely points to mixture.
Paul Walbran

Hi Paul x 2

P1 = Yes - The external resistor coil will naturally need a resistor of some description I would have thought that would have been understood but in hindsight I should have mentioned that - my bad there- That was what was behind my concours/purist comment The extra resistor block being maybee a concours problem to some ----not me
P1&2
The later starter isn't really needed, I just run a wire from the starter solenoid exciter wire with a nice healthy diode in it. Works fine, there is a very very small drop through the diode but still a good boost voltage for the ign coil
MGMike
Yes your wiring idea is as above and there isn't that much of a current draw on the wire as the coil is already being partly fed through the ballast resistor
Also it can be a bit confusing sometimes calling the coil a 6v coil, and it's also confusing that some of them are actually marked 12v on the bottom Really it is a 12v externally balanced coil
cheers willy
William Revit

MGMike
Just to clarify the starter issue---
As Paul W has mentioned the later type starter motor has an extra output terminal on the end of the solenoid cap
This terminal gives a separate battery voltage supply, only while the starter is being operated

cheers willy
William Revit

The 2M100 may have been used from 1971 but only from the start of rubber bumper production did it have the additional boost or ballast bypass contact.

"there isn't that much of a current draw on the wire as the coil is already being partly fed through the ballast resistor"

Not so, the whole point of bypassing the ballast resistor is that - with with a relay or solenoid bypass - there is no current at all flowing through the ballast, all the coil current passes through the bypass circuit. In normal running just under 5 amps is flowing through the ballast. This rises to nearly 7 amps in the factory bypass circuit with the 1.5 ohms 6v coil and a typical cranking voltage of 10v. Using a typical silicon diode there will probably be in the order of 1.2v dropped across the diode, so about 6 amps through that, and 1 amp through the ballast resistance. Ohms Law.

There is a huge amount of confusion around coils, including labelling, packaging, and with vendors, and that's before people throw 'internal ballast' into the mix. The only way to know what you have got is to measure it with an ohmmeter - about 3 ohms for a 12v coil, about 1.5 for a points 6v coil, about 1.4 ohms for a 45DE4 coil, and maybe as low as 0.8 ohms for a 45DM4 coil. You can use a higher resistance coil at the expense of loss of spark - significant with a 12v coil in place of any of the others. If you use a lower resistance coil with the exception of a 1.4 ohm in place of a 1.5 ohm, you will get coil overheating and points - if that is what you have - burning.
Paul Hunt

Paul
Yes mate I agree with what you're saying but I'm trying to keep it simple here without trying to confuse with too much techy info ,which is starting to happen a bit
Not all these guys on here are really interested in the tech side they just want a simple known fix which I thought I was trying to provide here-----

You picked up on my current draw statement and say the ballast resistor is bypassed
I think you are being a bit harsh on me
Yes the ballast is bypassed at cranking by supplying 12v to the coil end of the ballast but there is still an ignition feed to the other end of the ballast which in my way of thinking must help take some of the load
It's got me interested now
Job #1 for me is going to be to measure both while cranking - bwhen I get back to work
willy

John
Just get your mate to put a ballast resistor coil and resistor on it Repco's got em in a kit
He'll know how to hook it up or if he doesn't take it in to Shorty --- cheers
William Revit

The Unipart fische list the same part no for all 2M100 solenoids from introduction to end of production. Generally they are quite thorough with supercessions and don't airbrush out earlier versions later changed.

The amount of current flowing through the bypass is not really the issue. What matters is the voltage the coil sees while the engine is being cranked. Though not as good as a relay bypass, even at 1.2V lost across the diode the outcome will still be well better that an unballasted coil and installation would be a quicker and simpler retrofit.
Paul Walbran

Getting back to the colour of the plugs. Are these checked with the air filters on. It's going back over 40 years, but I bought a Sunbeam H120. Although having a full service history the Air filter had never been changed by the look of it. On the day I picked it up it acheived 4MPG. The plugs were black with metal specks. I took the head off and the tops of the pistons were pitted and the combustion chambers eaten away in places.
c cummins

As far as the solenoid goes yes you are correct, all 18V engine starters should have the bypass spade (smaller than standard) in addition to the standard-sized operate spade and maybe a large 12v spade on the battery cable terminal, although it wasn't used until rubber bumpers. I'd not noticed it on mine before.

But for the factory bypass, with 12v on both sides of the ballast - one side from the ignition supply and the other side from the bypass circuit - there cannot be any current passing through it as there is no potential difference across it - no voltage, to current.

Whilst it's true that under very adverse conditions such as weak battery, poor state of tune etc. the ballasted ignition system probably does mean the difference between starting and not starting, but in my experience not much. My V8 (all of which had ballasted ignition, chrome bumper and rubber) has had occasional hot starting problems this summer, and as on one of them I could smell fuel I knew it wasn't lack of that, so wondered about the bypass circuit. Tested for it, and no bypass. Investigated it, found the wire broken. Fixed it and tested it, still no bypass, even at the solenoid spade. So I dismantled the solenoid and found the bypass contact bent away from the copper bar (arrowed in the attached), so it had never worked since I replaced the starter 15 years ago.


Paul Hunt

Agree that when everything is right ballasted ignition isn't needed. But in practice, sub-optimal conditions do occur from time to time. In aprticular, people who rely on their car every day (there are still some) find great value in the extra reserve of a ballasted set-up, especially if they have to park outside in damp conditions.
Paul Walbran

Well, yes, and that is what I said. My 64 Mini didn't start one horrible cold and damp morning. So I pulled the lead out of the coil by about 1/4" and got the wife to crank it, and it fired up straight away.

But how many chrome bumper cars were manufactured? And how many other BL models used the same unballasted system? There have been many complaints thrown at BL over the years but hard starting of the MGB and its ilk isn't one of them.
Paul Hunt

After being away for 5 weeks, i installed the new NGK plugs, Pulled the choke, cranked, and she started. After warming up, I adjusted the jets and took her for a run. No sign of any hesitation under load, and revs freely.
Next step is to take it to a local expert who is experienced at balancing SUs. The thin dash pot oil didn't seem to cause any initial hesitation under throttle but I can change that later.
After that I will enjoy summer and pull the plugs out for a look in a month or two. I really don't think I have coil or solenoid issues but will keep an open mind if problems resurface.
Thanks again for advice!
John Minchin

you may wish to take a look at articles such as these which may help you to diagnose your plug condition.

http://honda-tech.com/forced-induction-16/***-basics-reading-spark-plug***-3063102/

http://www.zumaforums.net/phpBB3/viewtopic.php?f=39&t=25039

if the white deposits are what the first article describes as 'diamond like' and the information given is substantiated, then you may wish to consider it's recommendations.
G
Graham Moore

Thanks Graham
Lots of good info in here - and I always thought spark plugs were simple devices!!
I will pull the (new NGK) plugs after the next good run and have a look before doing any "re-tuning"

cheers
John
John Minchin

This thread was discussed between 12/11/2014 and 26/12/2014

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