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MG MGB Technical - Electronic ignition

Hi folks, I'm thinking of changing my distributor for a new one with electronic ignition, I have a 1967 MGBGT, any thoughts on this, anyone changed one recently ie: acuspark do one, you get disi, leads, and coil all for £60 + pounds etc. hope for some info and help, cheers Jack.
Jack New Forest

Why don't you just use the original with a pertronix setup, and coil...
I've done that on two "B's", and it worked great.
E.B. Wesson

Thanks Ed I'll have a look at that Petronix

cheers Jack.
Jack New Forest

The Accuspark works well. with a new dizzy you replace the often worn out advance mechanism. Excellent value for money at the lower cost end of the scale.
jim soutar

Thanks Jim, that's what I was thinking good value, not a lot to go wrong, and you get a new dizzy, no brainer, cheers Jack.
Jack New Forest

Or go for the new programmable 123. yes, expensive but you get what you pays for! Mike
J.M. Doust

If your distributor is still in good condition, you can just get the accuspark module and insert it in your distributor.
Ted Mack

Hi Jack,

I support Ted's comment.
I have a Pertonix on my B which had a known good distributor. I have a 123 Tune on my C where the distributor was u/s.
Both work well but you will never match a 123 for accuracy with an old distributor. If you need a new distributor a 123 may be cheaper


T J Malloch

Now here is another query; Can one use an MSD Multiple spark capacitive discharge unit with a 123? The best of all worlds I would imagine? Mike
J.M. Doust

Electronic ignition systems either work or they don't, they do fail, and when they have the only diagnosis you can do is replacement. At least with points you can easily diagnose the fault and replace at the roadside, and I've never had points or condenser fail in over 40 years.

123 plus MSD? Double the trouble! In fact worse than that as when the spark fails you won't know which half is causing it.
PaulH Solihull

I'm not an advocate of MSD. Expensive for no if not negative effect. Read a very imformative piece on capacitive discharge where it compared spark energy and duration. CD didn't come out al all well. You can only burn the mixture once. The right mixture, the right compression and a fat, timed spark. What else do you need? But I've never agreed with Paul about electronic ignition. Go for it, with a good coil. The 123 should be much better for not having to rely on springs and bob weights for ignition advance.
Allan Reeling

Hi Jack
I've had my 1980 MGB from new and changed from old distributor this spring after considerable problems with traditional points (Had 3 sets all purporting to have the same ref number,but all different). Fitted a 123 and all problems went away,much smoother running,quicker pick up and better fuel economy.I reckon the car goes better now than it has ever done.

Hi Mike, Alan,

I agree with Alan that if you have a 123 anything else is a waste of time (and money).

A MSD unit is a capacitive discharge system (CDI). The multi spark feature is to ensure that the fuel is ignited. Because CDI has a very short duration spark, there is a chance that it won't fire the fuel, hence extra sparks to ensure that one of them will fire.

I ran a homemade, points fired, CDI, from Wireless World in the early 70s, for 4 years in a Morris 1500 and then for 14 years in a Golf (Rabbit). In the construction notes and elsewhere, it was recommended that the spark plug gap be widened to about 40 thou, to increase the chance that fuel is in the gap when fired. I did this and the 1500 needed much less choke, like 1/2 mile instead of 3 or 4 miles. Nothing noticeable with the Golf, but it had an automatic choke.
Being the type that believes in not fixing anything that isn't broke, I only checked the plugs every year or two. The gap had invariably opened to about 80 thou, without any noticeable effect on performance. I know that higher voltages were produced, but as said there was no problem. In fact when I sold the Golf and retrieved the CDI unit I had a lot of trouble getting it to run with standard ignition, like the points needed cleaning, the plugs needed to be reset to 25 thou, etc.

Herb Adler

I have no doubt that the 123 distributor is good, so it should be at the price.
Ihave been useing the petronix for 5 years now and it has been very good and was very good value for money as it was a third of the price of anything else at the time.
A friend of mine fitted one of these replacement dizzys with electronics in and he has been very pleased with it. Go for it ,you wont be dissapointed.
Trevor Harvey

Trouble is that a large part of the cost of a 123 is in producing the original curves, and they are no longer relevant with today's fuels, so much so that some vendors recommend the generic version for the MGB rather than the MGB-specific version. Good stuff will always work better than knackered/incorrect stuff, and that goes for good points over incorrect electronic as been reported here in the past, including new distributors (and what curve do they have?) fitted with certain under-cap triggers that fire the spark when the rotor is between contacts. I've used CD in the past and found no detectable difference over correctly setup points, so much so that when I sold the car it was fitted to I took it off but have never bothered refitting it.
PaulH Solihull

About 10 years ago I put the Crane electronic unit in my 71 B to get more reliable performance, hotter spark, better timing stability etc. In the last few months, the car was difficult to start with the choke engaged, the tach started randomly red lining, and the engine lacked zip.

About a week ago it finally and suddenly quit altogether. The first time since 1995 that I was stranded. What quit? The Crane electronic module. New points and condenser later and it starts better, runs stronger, and if it fails, will probably fail slowly so I would notice and likely not get stranded again.

I should have left well enough alone.
G Nicholas

My MGA has a 3 Bearing MGB engine fitted which has been bored out to over 1900 cc and stage 1 tuned.
3 years ago I fitted a Pertronix distributor (Ignitor II with no vacuum advance)to overcome some slight misfire problems and this really improved the running of the engine and vastly improved the starting.

Today I tried to start the car but couldnt get a spark and in the end I have had to fit a new distributor to get it to run.

Does anyone know how I can test the circuits on the faulty dizzy to see if I can determine what is wrong with it.


Colyn Firth

Colyn Firth

Electronic ignition,iwould not not have any of these bolt kits given, i have driven over 500,000 miles in B series engined cars with points ignition over the years, and have never ever had a problem, i buy 1 set of points (land rover OE) for less than £2.00 a year,set the dwell dab of grease on the cam loabs and thats it untill next year, i get over 30 MPG and performance is better than what the workshop manual gives,and if i did have a problem i can fix it on the side of the road,so no thanks, A.T
andy tilney

Yes but,,but ,, but,, all the racing aficionados have got non standard kit that has to be better. Some-one has just sold me some stripes, you know stick on thingies and they lower the coefficient of friction where-ever you put them, so you can balance stiff steering etc jolly good stuff...... Yes I am pulling your plonkers.
There will always be a balance. New tecnology need not frighten us off. If the original works, don't change without good reason. Mike
J.M. Doust

Ditto AT. Never had points or condenser fail on anything in 45 years. For a bit of fun I ran a set for over 15k before I started noticing cold starting on the roadster was taking a bit longer. The old set weren't even pitted/spiked. A similar distance on the V8 showed no change, but I splashed out and replaced them anyway. As far as plugs go I put a set of Bosch 4-point in the roadster 25k ago and they are still going strong, got 40mpg travelling up to Newcastle last weekend. I did change the plugs in the V8 this week as hot starting had suddenly become more difficult, and they had also done a good 25k. Leaving the roadster plugs alone was intentional, but I must admit I had forgotten all about the V8 plugs. Still no sign of erosion on them, but changing them has brought instant hot starting back again.

You can only really diagnose electronic ignition, especially under-cap things like Pertronix by substitution i.e. buying a new one. If the distributor whizzing the magnet past the sensor isn't producing voltage changes at the coil then there isn't much more you can do, unlike points. It could just be the conductors fractured inside the insulation where the leads go through the distributor body, these are continually being bent back and fore under vacuum advance as your throttle position changes, but even if that were the case you would have to splice the wires inside the distributor, which isn't going to create a very reliable repair.
PaulH Solihull

My 67 car is still +ve earth. This restricts the choice of electronic ignition. I have in the past fitted a Pirahna and a Jolleyes "Classicheads" when they worked they were fine, but service life was very short, about 2 years, and neither vendor was interested in the product after that time. So I cant recommend either. The main reason I went for electronic was the shockingly poor quality of the far eastern sourced capacitors.
I now have a Boyer Bransden assisted ignition, for +ve earth you do not have a capacitor in the dissi, and it works well. After being burned so often I also have an externally mounted competion capacitor. I can take the amplifier out of circuit and plug in the cap via spade terminals at the road side. So far I havent had to do this.
Peterr Burgess posted on here that he is going to be offering an external high grade capacitor, a lot cheaper than the one I got. They come in a little case with a mounting clip BTW.
Stan Best

We have a GT and had 123 fitted.
Was not happy about it!!

Changing curves is a pig
the curves do not match the original
Fuel economy was down
The advance mechanisme creates a lot of rotor/cap wear

Switched back to the old dissy with a simonbbc (google that) electronic unit and it is top again.
The unit is cheap as chips and it works like a charm.
Cheap enough to carry a spare unit.
Fit it with one of their good rotors and caps and you will be on your way.
We have done 9000 miles with it and it is flawless.
I know of others who have driven a lot more and it still is fit and forget.

My vote as long as you are happy with your curve fit one of these cheap units.

123 is fun for a tuned engine and then you need the 123 tune with complete adjustable curves and not 16 curves that just do not cut it.
But the 123 tune would need some roling road time
Onno Könemann

Ah well, I'm rightly or wrongly on my third. The first didn't work at all. The second lasted about two months and then failed on the MOT ramp the third I kind of landed with by ordering an electronic unit from MGB Hive only to discover that it was a Simonbloc when I received it. Nevertheless it has been fitted for a couple of months now and seems to be OK. This unit is on my roadster and on my GT have a Magnetronic fitted for about ten years without any problems at all.

I will reserve judgement on this latest acquisition until it has had time to proove itself.
Iain MacKintosh

We all seem to be arguing for and against modern electronics, the fact is the tecnology is here to stay. As we all get older, and parts become more scarce, what are our children to do ( cause I will be 6 foot under!) Look at TV sets or 'flat screens'. They don't break down that often now. Some ignition units are failing when the old systems went on regardless, but the fault is not the design rather component selection, dare I say quality control. The old systems were probably turned out virtually by hand in the old days, good quality. Today depending on source and origin, who knows what the quality, and hence longevity will be like. Look at that huge Bugatti, bet it has electronic ignition! Mike
J.M. Doust

Well, I guess it has all been said, but I will add my 2 cents anyway.

I must say putting a Petronix in my 72B has made it start and run smoother than ever. It was very simple to install and I have the points and condenser at hand should I need to change back quickly.

At my age I don't enjoy bending over and peering at points as I try to adjust them. Even seeing to put them in is a bit more of a struggle than it once was.

I would consider a more expensive set but the Petronix has served me well.
John Lifsey

This thread was discussed between 13/08/2011 and 17/09/2011

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