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MG Midget and Sprite Technical - Midget 1500 misfires

my 77 1500 misfires after a 5 minute switch off following a 20 mile drive, I thought the points had closed up, adjusted them all fine it ran well,but it's done it again, points ok , any ideas ?

Hi Scott, welcome,
a bit more info might help others (not me though).

Have you serviced the car and/or added any new parts just before your misfire?

Have you set the tappets, (points), plugs, timing and carb mixture, in that order?

Do you mean after a 20 mile drive, then switching off for 5 minutes, on restarting you get a misfire, or have I misunderstood?
Nigel Atkins

Definitely more information needed here Scott, as Nigel said.
At the moment the list of possibilities is endless and, much as some of us enjoy the stab-in-the-dark approach for a bit of fun, it won't help you much.
Have you changed anything recently?
Does anything get notably hot?
Do you have spare ignition parts for testing by substitution?
Is your ignition system original? (Probably since you mentioned points).
Either way welcome to the board.
Greybeard's worth checking the internal LT wire in the distributor. I had an annoying misfire on my 1275 which was finally traced here..the external insulation was intact ...but the wire inside had broken..
David Cox

i all, thanks for the feedback, I haven't changed anything apart from trying a new rotor arm, that didn't make any difference so I put the old one back on. After it did it the first time I checked the points , I reset them that seemed to cure it, yesterday however it misfired again after a 2 minute switch off. Started it this morning perfectly ok ?
The only things I've replaced are 2 hoses from carb to metal pipe and breather hoses
Scott Coe

Something you could try which often helps is to have a look in the dark while it's misfiring. If you're lucky you might see sparks where there shouldn't be any, which means something is breaking down and earthing when it's hot.
The usual suspects for that shenanigans are HT leads and cracks in the dizzy cap.
You might get lucky and it's surprising how often it works.

(It's also how I set my Cortina on fire because I forgot to tell my sister to switch off before I hit it with the WD40 - - - don't say I didn't tell you hahaha!)

When it is misfiring, does the rev counter needle jump around erratically? If so, it would indicate the fault as being electrical, and on the LT side of the ignition circuit. (Ignition switch, coil primary, points or any of the wires between)

If the rev counter is steady, or simply drops as the engine runs more slowly, then it's either an HT electrical fault (coil secondary, dizzy cap or rotor arm, plugs or plug leads) or its fuel or valve related.

To be honest Guy I didn't notice what the rev counter was doing, too busy trying to get it into my garage. I've had the car 6 weeks covered about 600 miles in it ( more than its covered in the last 10 years) and looking at past paper work it looks as if all the ignition stuff is at least 10 years old
Scott Coe

Yes, I know what you mean Scott, you end up fully focussed on nursing the car and don't get time to check stuff like that. But there is a lot one can do in terms of fault tracing without even getting out of the car - if you remember!

I'll do my best to remember that tip Guy thanks
Scott Coe

you're doing the right thing by getting the car used as this will help it and you to learn about it but it will throw up issues, particularly those from lack of use.

10 year old parts can sometimes be better than 10 minute old parts so you've done the right thing to hold on to the previous parts and if they're in good working condition putting them back on.

Try checking the points again they can certainly move around within 600 miles of being set especially if they are piss-poorly made set.

On top of what Grey has put about looking for sparks in the dark, we used to encourage them to stand out them by spraying around with light mists of wat, I'm not too sure if it was a good idea though.

If the car is new to you I always suggest buying, reading and referring to the Driver's Handbook as it contains so much information about driving, servicing and maintenance. Then to carry out a rolling 30K-mile service in between using the car all year round and not doing any unnecessary upgrades, improvements or cosmetics until at least 12 months of year round use - as you may need the money for more, possibly a lot more, servicing, maintenance and repairs than you expected.

Whereabouts in the fair county are you, as a Coe does your family hail from around desborough or Stanwick? Raunds areas.

Below is for earlier models but it will give you the idea of what's in the Driver's Handbook (owners Manual now).

Nigel Atkins

We were always encouraged to firmly grasp each of the HT wires in turn to detect for poor insulation.

One can also narrow down misfire faults by disconnecting each lead in turn from a running but misfiring engine. The one that doesn't make it run worse is the faulty cylinder.

Next task being to swap plugs around, and if necessary then swap leads as well and see if you can move the fault around.

>>We were always encouraged to firmly grasp each of the HT wires in turn to detect for poor insulation.<<
Whilst standing barefoot in a bowl of water or wearing rubber wellingtons(?).

If the spark plugs are 10 years old they'd be changed ASAP by me (and to NGK) as would 10 year old HT leads and . . .

Nigel Atkins

There is an awful lot written about the effects of pressure and sparking voltages. A spark from the end of an HT lead need not automatically lead to a spark at the plug under compression. Always worth changing, as Nigel says.Dave
David Cox

Disconnecting leads with the engine running is not recommended if you have an electronic ignition as it can damage the electronics.
David Billington

I think Scott mentioned having points?

Changing plugs and leads just because they are 10 years old is a waste of time when it may not be a plug fault anyway. Much better to pin point the fault by elimination and logic than try the scatter gun approach. Especially as new plugs are known to occasionally be faulty straight out of the packet.

Hi all, thanks for all the tips thoroughly enjoying using it, Nigel I live in sunny Desborough, I have a handbook but thanks anyway, I was thinking of getting the necessary bits from the distributor doctor as I believe they're quality stuff and go from there.
Scott Coe

"Disconnecting leads with the engine running is not recommended if you have an electronic ignition as it can damage the electronics."

It can also damage you quite seriously. Ask Willy R.


OK, I was being intentionnally light on detail, just for fun! I do well recall Willy's experience though.
But the testing for stray electric escapes by clutching the connected HT leads in turn was exactly how I was shown how to check them at a garage I worked in the 1960's. For actually disconnecting plug leads from a running engine I would recommend using good quality insulated pliers. It is still one of the best ways of narrowing down where a misfire is occuring.

Another way is to use one of those laser spot infrared temperature guns. The misfiring cylinder will very likely show up as a slightly lower temp in the vicinity of the plug.

I know this is a 1500 being talked about but one needs to be careful with some engines such as an A series on a side draught carb as the mixture is unevenly distributed and removing IIRC 1 and 4 leads from a running engine may have no noticeable effect to the running whereas removing 2 and 3 leads has a significant effect.
David Billington

Worth knowing about, but from that explanation if the misfire was from a failing plug on #1 or #4, then one wouldn't really notice it.

Desborough was going to be my first choice but you may be a generation or two after me.

Changing the 10 year old HT leads and plugs and other items was not just for fault finding it was part of the rolling servicing and maintenance and to get best performance. Even if they are working just material deteraition over 10 years would take them passed their best plus you don't know their history.

I take the idea that you get a small light sportscar for all the performance it's capable of otherwise if you just want it for show or occasional sunny Sunday afternoon bimbles that's a different matter.

If you wanted to find the exact fault location or cause you could literally fit the new plugs and leads (and ect.) one at a time with the existing plugs and leads (and ect.).

Yes Dissy Doc for good reliable dissy parts. You sound as if you've already learnt a bit about classics, having a Driver's Handbook puts you ahead of many even long term owners. I also take it you knew Guy and I were joking about handling live HT leads, Willy will certainly be able to tell you about proper safety measures and why they are required.

Had I not been working on my midget yesterday, something I loathe, I could have gone out for a roof down run as it dried up in the afternoon around here, same as Saturday. I unlike most posters here only enjoy driving my Midget, year round, I only do any work because its routine servicing, maintenance or repairs which will keep the car performing well and safely.

We sometimes pass through the edge of Desborough on some of our runs but never stop as there's no decent real ale for us in the town. Although we did call into The Geogre years ago, the days when you could book an appointment for a fight, the town is a bit more upmarket now.

Nigel Atkins

I'm with you, Nigel...I drive my Midget all year round.

<< I only do any work because its routine servicing, maintenance or repairs which will keep the car performing well and safely. >>

is there anything else to do?? Dave
David Cox

Well you've done something I've never done, gone into The George and I've lived here all my life (47 years) !!
I've got a Moggy 1000 had it 20 years had various niggles over the years but nothing like this one, I think I'll just swap bits from the DD and see how we go.
Are there any MG meets around Northants ?
Scott Coe

"Guy and I were joking about handling live HT leads"

No, I wasn't joking Nigel. That WAS how I was shown how to do it when I worked at a garage in the '60s.! I still do, on occasions, though I admit I just brush my fingers lightly across suspect HT cables, rather than "grasp them firmly" !

But that isn't to say I recommend it. Grey's advice about looking after dark for sparks and traces of light is definitely a better and less painful method.

I'm sure you were told to grab the leads but I hope you'd be joking now. We did use to spray with water. There are lots of things we done decades ago and when young that now know were stupid, macho, ill-advised and potentially dangerous. I'm sure you like me have scars, aches and pains from doing some of those.
Nigel Atkins

to be honest on more thought it was my wife that went in The George once during the 'caravan club' days, I only went later when it was quite respectable, well in comparison.

I'm 59 and old enough to have been to The Ritz when it really was a ballroom (but I was only a young lad then).

Of course the misfire may not be from what you replace but if you insist on remaining with points then best to get them from DD and certainly if you want the original and better quality 'red rotor arms'. I've had problems with dissy caps in the past too. Problems in parts are not always noticeable to the naked eye.

Moggies are lovely, A-series as opposed to Triumph engine as you have in your Midget and as I have found on here over the years (and having GT6 for a while) there are a lot of differences in the two engines and their running.

I don't go to meets much I prefer runs although I did go to a MASC (Midget and Sprite Club) meet in July (IIRC), I was hoping that those attending would swap rides in the cars so that those new to classics or the model would be able to compare the way the cars drive, one lad who thought his clutch was soft feeling when it was was the heaviest on a Spridget I've ever known certainly needed a run in a different car but it didn't happen and I was unable to go to following meets to offer.

For various and shiny cars parked up in a field there's the A45 Earls Barton meet, I've never been despite my club locals going there (Shire Bears of the Sporting Bears Motor Club), I'd sooner be at the Saxon Tavern, anyway it's far too close to me to even get the coolant warm.

The Northants MGOC (semi-autonomas) club must meet somewhere, the Kettering Area used to be, so I was told, four non-owners that meet in a pub, I'm not sure if they still exist.

I've been trying to organise an informal Spridget run in Northants and possibly including South Leicester, Rutland, Warwickshire but not necessarily all at once but finding the weather reasonable, people available and cars working all at the same time takes time.

My wife is good at sorting ad-hoc runs and as you know there are some great roads in the county and almost traffic free at the right times. If you're interested in a run just let me know. We also have great roof down runs in winter, dry and often sunny.

MASC Northamptonshire Meet -

Northants MGOC -

Earls Barton Meet (stops in Sept tho') -
Nigel Atkins

Well, there's a turn up. I'm going to have to agree with Nigel.
Back in the day when I lurched about in a series of grungy Fords which were all I could afford, I would routinely replace plugs, leads, rotor, points, condenser and dizzy cap when I bought another car. Sometimes coil too, not forgetting to resite it from the stupid place Ford fitted them just inside the grille.
Without fail it made a notable difference, probably because they were so badly neglected by the POs.
However they were original quality spares then, not the garbage so common now. (Distributor Doctor excepted).

Like Guy I used to grasp and wiggle HT leads, but I got righteously zapped many times for my pains. Not sure if my ancient heart is still up to it! A Mk1 eyeball in a dark garage is my preferred first step now.

Nigel mentioned water mist - I've never done it but I have heard it's effective.

I think wasnt saying not to fit new plugs and leads. What I was suggesting was to narrow down the fault by a series of tests and swapping around of parts. That is the best way of isolating and identifying a problem, at low or zero cost, which can then be corrected.

If the car needs a service, then by all means do one but if you don't isolate the problem first you could find yourself no further forward after spending a significant sum,possibly quite unnecessarily.

Often it's the poor way I put things but I am often agreeing with others on here and other sections, However it's becoming an epidemic today, you and Paul Hunt and I agreeing - thankfully there's always CB points, relays, oils and the 'joy' or otherwise of working on the car to disagree about.

I've also found these ancient engines benefit from regular servicing particularly air filter cleaning/changing and oil and filter changes if you want better and consistent performance.

Which is why I try to use parts and components that can reduce the list of service replacement items and oils that increase the change intervals (as well as offering wider and better protection). I wish I could reduce the use of the grease gun to zero though.
Nigel Atkins

Nigel, I like a run in the car to, so when you organise one send us a message
Scott Coe

Sure Scott, just email me your email address, my address above.
Nigel Atkins

This thread was discussed between 12/10/2019 and 15/10/2019

MG Midget and Sprite Technical index

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