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MG Midget and Sprite Technical - Intermittent Fault - spluttering

Hi All,

Looking for some advice on our 1973 midget

The fault I had with the Midget appears to have returned, post works, and it appears to be intermittent.

Wondered if anyone might have any ideas...


After a few hundred meters the car cuts out and judders. Other times it's perfectly fine.

When it cuts out it will restart, but then there isn't enough power to pull away and so cuts out again

AA come out and checked it. Carburetors were fine, coil and wires all fine, starter motor temperamental, but working, but apparently not the cause (will change that)

The spark plugs, all were black at the end, which apparently maybe because we're using the choke too much?

Carbs, fuel pump or vacuum leak were my thoughts, particularly after reading this article:https://www.2carpros.com/questions/mg-midget-1975-mg-midget-sputtering-engine-when-warm

Any suggestion as to what else to check would be welcome?

Many thanks,
Andrew
A Jeyarajah

Andrew, what type of rotor arm do you have? If it has a rivet on the top, it could be at fault.
A genuine red rotor arm from someone like the Distributor Doctor
http://www.distributordoctor.com/red-rotor-arms.html
may help and is a good idea in any case.
Others will have other suggestions for you to check!
Jeremy MkIII

Hi Andrew, welcome.

Could be so many things but always start with the basics. Just thoughts and questions from me now.

Have you fitted any new parts recently?

What works were done?

Has the car previously been laid up for a long time?

Is the whole car regularly and timely fully serviced and maintained?

Did you try pulling the choke out as it juddered?

Did you notice if the tacho needle was twitching?

Have you checked the flow rate of the petrol getting to the carbs?

Checked for any loose electrical connections and earths?

If the carbs are OK I wouldn't read too much into black plugs because unless you're only using the car for short runs (never good) then when you drive it as designed it should blow the plugs clear from using the choke.

Intermittent problems are always a pain, are there any circumstances when you get the problem, engine, hot/cold, weather hot/cold/wet, etc., etc.?
Nigel Atkins

Another thought - does the fuel tank have have fresh recent petrol or stuff from months ago or could appear on Antiques Roadshow?

If you could put up good photos of your engine bay (preferable taken and posted in correct landscape orientation to save straining necks) it could give some useful info.
Nigel Atkins

It isn't a Midget, but I had a similar problem with my Triumph Dolomite 1850 running on SU carbs. It sounds like a fuelling issue, ie not enough fuel getting into the engine. On my Dolly it was caused by the Waxstat jets in the carbs. It ran great when cold, but after a couple of miles it got worse and worse, until flat out in 4th gear it couldn't keep up 40 mph and cut out as soon as the clutch was pressed.

These waxstat capsules open up as they get hot, weakening the mixture. They might have worked once when new and when fuel was 99 octane leaded, but once I had swapped them for plain jets the car ran beautifully.

I'm not sure if a '73 Midget would have had waxstats, but to me it definitely sounds like the mixture is too weak. Have you got any air leaks on the inlet manifold?
Mike Howlett

If you have a points & condenser set up, I suggest the condenser is a good place to start. They are a well known culprit for failure

Cheers

Gary
79 MGB
Gary Hansen

Hi Jeremy, Nigel and Mike,

Thanks you all very much for taking the time to respond. Its all genuinely really helpful

The car is currently at the mechanic, but i'll try and get some images sent over (and will copy this thread over to him).

Jeremy - I'm not sure of the colour of the rotor arm, but i'm pretty sure its not red, so i'll investigate DD.

Nigel - This fault initially occurred the day we purchased it, (we've owned it for about a month now, as did the previous owner it transpires). MOT last done in Jan 20, but we've recently redone it and it passed.

Prior to our MOT we drove back from Sommerset (where we purchased it) to Herts and refueled on the way on a couple of times. First got this issue on day 1, but it restarted after a short stop so thought nothing more of it. Subsequently at a car show the same fault reappeared. Someone else noted an inspection slit in the wiring leading to coil. This was subsequently checked, with our garage, but found not to be at fault (other issues were break pads and axel related, those are resolved). A couple days ago we headed out and the car cut out again with a few hundred meters and wouldn't restart (hence the AA and my current position)

No new parts have been fitted since our ownership.On the last occasion, the car still juddered under choke. I didn't note the tacho needle and haven't yet checked the flow rate into the carbs.

Mike- I'll check the carbs, its does sound similar, but i'm not sure why the fault would only be intermittent in this case.

Gary - Someone else i know with a Midget also suggested the condenser. I wasn't actually aware of this component, so will check also.

Many thanks again....I agree intermittent faults are a pain!
A Jeyarajah

..also meant to ask, can any recommend a supplier for a "reliable" replacement condenser and stater motor?

Many thanks
Andrew
A Jeyarajah

Andrew

What is actually wrong with the starter?
Bill Bretherton

For distributor parts the most reliable source is undoubtedly the Distributor Doctor. He can supply anything for Lucas distributors from points, rotor arms, condensors to full recon units. Check out his website. http://www.distributordoctor.com/
Mike Howlett

Andrew, thanks for replying.

I'll start with the miserable bit first.

What you need to know is that many modern made classic parts are crap, some abysmal, some just poor, these include things like condensers, and many ignition parts. Just about all the suppliers big and small sell some or lots.

There some good quality parts that are available as an alternative, even offered with the crap versions, but many (most?) classic car owns are too tight-fisted to pay sometimes the very small amount extra for the better quality parts.

Now if the previous owner only had the car for a month and fitted any parts then they may be the cheaper crap parts so have a look if you have any receipts.

Getting an MoT done is a good idea but you must bear in mind this only means the car met a minimum standard of road worthiness to one qualified person's opinion at one moment in time, it doesn't mean the car is or goes as good as it could or should.

If you need to swap out any dissy parts then the Dissy Doc is the place to go, but it's too early to say what the cause of your problem is, dissy cap and/or HT leads can do funny things too.

Good news, you driving the car all that way and since is good, they really need regular reasonable distance runs all year round otherwise they can get faults from lack of use, as you might be discovering.

Also good news you can have loads of info at your fingertips, not just here but by having, reading and referring to the good book, the relevant Driver's Handbook, if you do this you will know more about the car than many, even long term, owners.

If you're going to the Classic Motor Show I'll take you out for a 10-mile ride in my 1973 'go not show' 'it's not wot yer got but 'ow yer use it' Midget. 😁

Don't think about replacing the starter yet, you might not need to and it might even be related to this issue. You don't even need a starter if you park on a good slope or your partner doesn't mind pushing (whilst you steer). 😁

And don't worry too much about that article that you linked to as generally lots still applies the 1975 Midget had a Triumph engine, not an A-series like yours and since sometime in the 60s the USA cars had started varying quite a bit from UK models.






Nigel Atkins

Mike,
no Waxstats, at least this side of the border and it was 97 octane, all in the good book. 😁

Was the Dolly supposed to have been on 99 then?



Nigel Atkins

No Nigel, the Dolly was also recommended to use minimum 97 octane. My memory fooled me but the original 1977 owner's handbook put me right. I have been through the Midget parts book and it seems that waxstats were never used, which I find a bit surprising since the rubber bumper cars used a Triumph engine. The waxstats were introduced to try and get the exhause emissions down below a CO level of 4.5%. A tough job with SU carbs. With standard jets my Dolly is marginal when tested, but fortunately my MOT garage understands old cars and doesn't worry about it.

Anyway, back to Andrew's original problem, he first posted on the V8 register board and there has been a suggestion on there about the venting of the fuel tank. This is well worth checking. If a non-standard fuel cap has been fitted you need to check whether it is vented or not. Through the cap is the only way air can get in to replace the used fuel. If the cap is sealed then the pump won't be able to suck against the vacuum built up. Next time it happens, jump out and release the cap - you may hear a hiss as the air goes back in and then the car will run properly again.
Mike Howlett

I'd echo Mike and agree it sound like fuel. Strip the carbs, blow and clean everything out, check float height, check if float neeedle is seating correctly, and consider using a carb repair kit to replace O rings and gasket etc. Read the manual, reassemble, set everything according to manual, check for leaks using soapy water, try again.

Possibly fuel pump on its way out. Disconnect the feed at the carbs, use a jam jar to collect fuel. Again read the manual on this.
Oggers

Mike,
Waxstats did go on some 1500s though I'm not sure which ones.

I did think about the fuel cap as I like quick and easy checks but as I put there are so many possibilities and if the car is with a mechanic they'd check that (you hope).

I was trying to steer Andrew away from model variations like with that USA article, altho' of course I've no idea if he has a standard UK 1973 model.

I have more idea than usual this time as I have a factory original concours accurate (not) 1973 model myself.

And of course access to a (near) relevant copy of the good book!
Nigel Atkins

This thread was discussed between 25/10/2021 and 26/10/2021

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