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MG Midget and Sprite Technical - 1500 ignition woes

I've been chasing what I believe to be several problems with very similar symptoms, some have been corrected, some corrections have made things worse. Here is where I am now:

California spec 1500 with a Weber downdraft, and the OPUS ignition, coil with an internal ballast. These parts all on the car when I purchased it two months back.

I had an intermittent miss that seemed to correlate to fuel levels, I thought water in the tank as it would only happen below 1/4 tank. Then it started to happen at half a tank.

I purchased a new coil, new cap, new rotor. then I started to have random ignition cut out, the tach would die as well. Eventually I noticed a wire in the harness from which the insulation had melted, after disassembling the harness I found that the wire had been snipped on both ends and replaced BUT it had slightly damaged a few other wires, which I replaced.

The head to battery ground was also loose, I tightened that... realized that the new coil was the wrong type and reinstalled the original.

At that point I was left with a drastically reduced set of symptoms, hardly noticeable. Just an occasional miss under load, leaving plug 3 a bit sooty. The others seemed fine.

I adjusted my valves, set the timing, things were peachy for a bit. Then my fuel economy halved, down to about 12-15, new plugs and tuning the carb helped a bit. Static timing was still fine. Soon after economy dropped down to 10-12, car would barely accelerate to 60. New plugs, and checked the timing, it was way off, from 12 BTDC to 2 ATDC (the vac connection has long since been removed). I set it back to 12, things are improved but still bad.

The car has been this way for about a week now, in the past the problem would last a few minutes to two days...

Any suggestions? I'm a fuel injected, coil on plug sort of guy so I'm a bit lost but I suspect the distributer itself or perhaps the CEI box.


PMR Robles

The OPUS distributor/ignition was notoriously unreliable and I'm amazed to hear of one still in use. So, it's a distributor swap with contact breaker or a distributor with an aftermarket electronic conversion. I think Crane used to do some sort of conversion specific to the OPUS distributor.

Or it could be something else.

There are books with this stuff in ...

Daniel Thirteen-Twelve

That is what I have. Moss Motors sells them so no telling how old it is.

Inside beneath the rotor arm is a black disk, with 4 equidistant incisions around the edge, and a pivoting arrangement which I believe is what is actuated when the vacuum port is connected.

I'll post pictures tomorrow.
PMR Robles

Affectionately known as 'opeless, I believe!
Dave O'Neill 2


Did the car run without fault when you purchased it?

Did the wire repair fix the tacho problem?

Is the original ground strap (front bottom of engine) intact?

Are you saying that after setting the timing to 12 BTDC it went back to 2 ATDC or you found it at 2 ATDC on first check?

Swap ignition wires around to see if a different plug gets sooty.

I will vouch for the Moss Flamethrower dist./ignition swap for 1500, mine works quite well.

The Weber DGV out-of-box is already jetted pretty rich for the 1500, if the float is set wrong the fuel usage will be quite high, but would probably show up on all plugs.

fuel pumps can push too much fuel, overwhelming the float (ask me how I know).

Test your dist. mechanical advance, your timing mark should be at 30-32 or so BTDC at 3000+ rpm. I have mine at 16 BTDC, with no vac advance to get to 30-32 (with the Moss dist).

Good luck!

RJ Reeves

Patrick. The first thing is to identify the parts that you have in your ignition system. I have some significant problems understanding what we are discussing from your description.

First, you note that you have an "Opus" distributor (this is the Lucas 45DE4 distributor). Then, you question whether there may be a problem with the "CEI" box. The Lucas 45DE4 distributor does not have a CEI box. It does have a rectangular section, grafted onto the normal distributor body which holds the electrics. So, if there is a CEI box you do not have a Lucas 45DE4 distributor. Nor, does the Opus system use a chopper plate as you describe in your later posting. Thus, we need to determine, as closely as possible, what ignition system you are using if we are to offer suggestions of what the problem might be.

Second, you note, in your original post, that you are using a coil with an "internal ballast". The internal resistance, measured between the two low tension terminals of the coil, of a coil designed for full time 12V input is 3.1 to 3.5 ohms. The coils, used on the later MGBs (and probably on the later midgets) were designed to operate at a reduced input voltage of about 6 volts with a second wire coming directly from the starter which provided a full 12V input to the coil while the starter was cranking. This was supposed to provide a "hotter spark" on starting. When the ignition switch was turned to the "run" position, the starter solenoid was no longer energized, the 12v was no longer sent to the coil, and the engine ran on the 6V (nominal) input supplied to the coil through a resistance wire in the wiring loom.

There is no such thing, in MG land, as a "coil with internal ballast". In the US, you will see 6V coils marked "For 12V with external resistance". These types of coils, including the ones used on the MGs in the late 1970s, have an internal resistance of 1.43 to 1.58 ohms.

Do you have a copy of the wiring diagram for your year vehicle? (Remember, often the California specification differed from the "49 State" specification and you need a diagram specific to your car.

Do you have a copy of the factory workshop manual or just one of the generic, covers many years, manuals? An original factory manual, specific to your year, should cover the California specification where most other manuals do not.

We need to know what ignition system you really have, rather than what you thing you have. You do not have a functional Opus distributor system, You should not have an "internally ballasted coil", and the wire you replaced may have been the required resistance wire supplying reduced voltage to the coil when running.

Right now, all we can say is that the loss of tach function indicates a problem somewhere in the low tension circuit of the ignition system. But, whether that is the primary problem or only one of the problems, we cannot say until we actually know what you are running.

Les Bengtson

I wish I said what Les said! Does seem likely that your Opus might have that Crane conversion.

Les - have a click on the photo I attached (I promise it is not a book cover).
Daniel Thirteen-Twelve

Daniel. Good photo. Some years ago, I sent you a CEI distributor which does not have the box on the side. If you still have it available, a photo would allow Patrick to visually compare what he actually has in his car. On my 1979 MGB, purchased in November of 79, I had the Opus system go out within the first three months of ownership. It was replaced under warranty, but I do not remember what unit it was replaced with. Perhaps the newer Lucas 45DM4 "CEI" unit? Back then I had little time to work on my own cars and factory support was still available from some of the dealerships who remained in business.

As to the inner parts of Patrick's distributor they could be a Crane (Allison) conversion or a Lumenition Optronic (sp?) conversion which is what we found on my daughter's 77B. Both had a remotely mounted power board (block of aluminum with fins milled in it) while the MG CEI (GM HEI) system had an enclosed black box mounted, from memory on the MGB, under the coil or near the coil.

Patrick has an interesting problem which would be, for us, fun to play with. Much less fun when it is your car, however. But, we have all be there before, have we not?

Les Bengtson

3-wire Opus on right, 2-wire CEI on left.

Sounds like Patrick has multiple issues, i.e. more difficult (fun) to track down.

Interestingly, my 1979 parts car is loomed for the Opus unit, but my 1979 driver is not, and they are only 200 or so serial numbers apart.

RJ Reeves

I believe I have the Lumenition kit... I've tried posting up a lengthy reply about 15 times now with no luck, so this is a bit of a test.

Pictures will hopefully make up for my ignorance...

The sealant in the distributor is an easy thing to point to as the problem but perhaps not the actual cause.

I also found this archived thread:

Difference is that my issue happens throughout the rev range.
PMR Robles

Replacing the wires in the harness (fuel pump and 12v switched to the radio) and the returning to the original coil cured the random stalling and the tach issue.

I assumed the coil was internally ballasted due to its labeling, I've since learned that the resistance is done in the wiring. Do I have that right? Regardless I will measure both coils when I get home.

Posted 07 December 2010 at 02:29:07 UK time
RJ Reeves, California, USA

"Did the car run without fault when you purchased it?"
"Did the wire repair fix the tacho problem?"
"Is the original ground strap (front bottom of engine) intact?"
"Are you saying that after setting the timing to 12 BTDC it went back to 2 ATDC or you found it at 2 ATDC on first check?"
"Swap ignition wires around to see if a different plug gets sooty."
"I will vouch for the Moss Flamethrower dist./ignition swap for 1500, mine works quite well."

"Test your dist. mechanical advance, your timing mark should be at 30-32 or so BTDC at 3000+ rpm. I have mine at 16 BTDC, with no vac advance to get to 30-32 (with the Moss dist)."
PMR Robles

Patrick. You have the Allison Optical-Electric points replacement kit. The last one I saw was back in the mid 1970s. They were, later, bought out by Crane who offered the same kit. Yours was, probably, a replacement for the original, failed, Lucas 45DE4 internals, perhaps installed after 1980 when the US dealer network was terminated.

The coil you show as original is intended for full time 12V input. Hence, you may have some wiring changes in your system which provide the full time 12V to the coil. This is something you will have to check with a volt meter while the engine is running. If you are showing less than system voltage, somewhere in the 6 to 8 volt range on the input side, you need to use a coil marked 12 Volt for use with external resistor. If you are showing 13.5 to 14.5 volts (standard system voltage with the alternator engaged) your original coil is fine.

I have seen several cars wired to run full time 12 volt input using your type of coil. However, running a 12 volt coil at lower voltage will significantly decrease the coil's voltage output. This may be part of your problem. The coil's high voltage circuit builds up until there is sufficient voltage to fire the spark plug. In my tests, this is about 11K volts at idle or at cruise. When running the engine under load, a higher voltage is required and supplied by the coil. But, it may be that the coil you are using, if the input voltage of the low tension circuit is incorrect, cannot supply sufficient voltage resulting in a miss under load.

In any event, I would suggest that you consider a new distributor (I find the points type 45D4 easy to trouble shoot) of some form as your old components are probably only marginally reliable.

Les Bengtson

Hi Les,

Here is the inside of a DM4 (actually a 65DM4 rather than a 45DM4) though we don't need it now as you've identified what's inside the DE4 on Patrick's car. I'm actually not that proud of that photo and at some point I'll try and take something better.

I'd forgotten you gave me a DM4 - I'm not sure what I've done with it but do still have a brand new DM4 because I bought one off ebay really cheap as well as a new pickup assembly. I also bought an original Lucas ignition kit test and diagnostic kit that was not cheap but was the first one I'd ever seen. Subsequently I saw several sell or not sell for for a lot less than I'd paid for mine..

I still have a Microdynamics copy of the DM4!

Daniel Thirteen-Twelve

Thank you all for the help.

IF I under stand correctly this:

would replace the internals of my current distributor, do away with the external box, and potentially work with the coil currently installed. Is that right?

I'm a poor student (who chose the wrong car to buy as his only means of transportation) so the price point is appealing.

Additionally it is a hall effect unit so I could use it easily down the road if I go EFI on the car.
PMR Robles

Patrick. You can purchase the Ignitor kit from your local cheap parts store and pay less than from Moss. The company headquarters is in California.

To answer your question, yes, this should be a drop in kit and would replace the power strip from the Allison, along with the internals. But, you have a distributor which is, at a minimum 31 years old. How well the mechanical advance still works would have to be a consideration--most of them are worn and with stretched springs by now if the car has seen any use over the years.

There are several companies offering "rebuilt" distributors for these cars, places like AutoZone and Checker. Avoid them. They are junk. It would be better to have your existing unit rebuilt and there are several reliable shops familiar with the MG distributors and the mechanical advance curves necessary with our modern "blended" fuels. You might seek advise from them as to what would be the least expensive method of correcting your problem.

In the mean time, figure out what the input voltage to your coil is. It is important.

Les Bengtson

Patrick. Here is a link to one company with a very good reputation for MG distributor rebuilds:

You may wish to shoot Jeff an e-mail about what can be done for your dizzy.

Les Bengtson

Thank you everyone for the help.

As it sits now I went out on a limb and purchased the pertronix kit, installation would have been straight forward except that the trigger wheel that was on the car was epoxied in place. I assume the installer lost the c-clip and didn't fancy a trip to the store...

Car pulls cleanly throughout the RPM band now, at rest and under load but the fuel economy is still dreadful. I've gone through 2 tanks at around 10 MPG. If I go any leaner with the mixture I get the issues mentioned in this link:

Backfiring through the air cleaner and hesitation in the 2-3k range.

Also to get in that 30-32 degree range above 3k RPM I end up at around 20 degrees at 1K RPM, come next month I'll give Advanced Distributors a call for sure and get a rebuild kit for the Weber.

Does anyone have any tips on tuning the carb? It seems pretty straight forward but I don't want to assume it to be as easy as it seems. I'm thinking a pressure regulator or different jets might be in order.

Thanks again.


PMR Robles


I have the same carb on my 1500. after swapping an older (mechanical) fuel pump with a new unit I was drowning in fuel with horrific mileage as well. No amount of tuning (idle and mixture) alleviated the rich running. After installing a fuel pressure regulator the problem was solved. It's also possible that your float setting is incorrect which will give similar, less drastic symptoms.

The Weber DGV is an eminently tunable, fun to play with carb when you get to know it. Given your gas mileage, I would bet your problem is as described above, not with your jetting, unless your PO made some colossally poor jetting choices.

After you correct the drowning problem you can make a quick (minor) improvement in mileage by: swapping the idle jets around i.e. put the 50 in the primary circuit and the 55 in the secondary. For a bit more lean you can swap the main jets around i.e. put the 135 in the primary, and the 140 in the secondary. This will make it a tad rich when over 2/3 throttle, but how often are you there really? This all assumes your carb is still jetted as from the factory for midget 1500:

idle 55
main 140
air 165
idle 50
main 135
air 160

With the DGV, at cruise the car is running almost exclusively on the idle circuit, not the primary, so this is where you can really improve overall mileage with some judicious tweaking. I am currently running a 47 idle jet in the primary. my AFR gauge tells me I'm a bit too lean at cruise, I'll probably go back to the 50 when I get around to it.

Pegasus Auto Racing has everything you need and more for your carb, they are online and located in Milwaukee, WI. No affiliation, just like their service.

RJ Reeves

I just rigged up an inline restrictor type regulator and with it almost completely closed the fuel smell is gone during a quick spin around the block.

Hopefully this will be the fix...

Now coming from EFI as I do a returnless system scares me a bit, I worry about lines popping off and pumps burning out. Is that not a concern? Looking around I see that many of the regulators lack any provisions for a return line.

PMR Robles

I'm dumb enough to not know what a restrictor-regulator is, but restricting alone I would think controls volume, not pressure (?), so you might expect the symptoms of excess fuel to be present at idle situations (smelling it at the red light), but running out of OOMPH! when heavy on the gas pedal for more than a minute or so (long enough to drain the fuel reservoir and lean out).

Curious to know what you find.
RJ Reeves

Just a bit of clarification regarding a statement Les made above:

>>> ...a second wire coming directly from the starter which provided a full 12V input to the coil... <<<

I'm sure he meant to say, "coming directly from the starter solenoid," unless I'm not remembering correctly. There should be two wires that connect to the coil's positive terminal, both white with a light green tracer. As described, one supplies a full 12V during cranking - that's the one that comes from the solenoid - and the other supplies the lesser voltage through a resistance wire in the loom once you've let the key back to the run position.

Also, I gather that you're running an aftermarket electric fuel pump, vs. the original mechanical type. Right, those can generate enough oomph to overcome the float valve in the carb. Have you tried one of those inline regulators with the adjustment dial on top? You can try different settings until you find the sweet spot.

On a different note, my '78 1500 has a now-unused wire carrying 12V (switched from the ignition) that used to supply power to the original distributor. It would have been connected to an external resistor, not to be confused with a coil ballast, and from there to the distributor. If you have such a wire, it can be used to feed a full-time 12V coil, if that's what you actually have.

Good luck, and keep us posted. I've been fiddling with my 1500 for over 15 years now, and am very interested in discussions of this sort.


Gryf Ketcherside

This thread was discussed between 06/12/2010 and 24/12/2010

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