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MG Midget and Sprite Technical - Engine cuts out when under heavy braking

Hi, I have a 1971 midget, had it for about 17 years or so, I've had most of the problems related to to our beloved obsessions and managed to muddle through and sort them out.
But the latest problem has me stumped, considering I've been pottering with old bits of tin for more years than I care to remember I've never come across this problem before.
A couple of weeks ago I unwrapped 'Old Allsorts' from her winter hibernation, took her out for a run, every thing was fine, which in its self was unusual, until I approached a line of traffic which was stationary, coming to a fairly quick stop from doing about 40 mph, and the engine cut out, trying to turn it over it sounded as if the battery was dead, after 3 or 4 turns she burst into life and away we went, about a quarter of a mile down the road she started to misfire for about 10 / 15 seconds then run great for another 10 minutes until we reached home.
I checked plugs, leads, fuel supply, tested for slipping clutch, bad connections, found nothing out of order.
Two days ago the same thing happened, after she had been running for about 10 minutes, checked everything again without finding a fault.
I've looked in the archives but can't find anything relating to this problem, if there is something in the archives can someone point me in the right direction.
Otherwise I would welcome any suggestions on what the problem may be.
Thanks in anticipation.
John.
J Elliott

I would consider checking a ground strap.
Sudden slowing down can make it loose contact.
SANDY

X2 sandy

And id add ignition wire shorting out...check for worn out connection at the coil, and the dissy, have a look at the ground wire inside the dissy, after 30 min grab hold of the coil fairly tightly... is it extremely hot?

Pull the neg cable off the battry completely and have a look for the greenish white powder inside the windings of the bat. Cable

Im thinking somekind of grounding issue

Prop
Prop and the Blackhole Midget

Have you tried the condenser. Mine went bad after the winter hibernation
Bob Beaumont

Thanks for your replies, Sandy, Prop and Bob.
The earth lead sounds like a possibility, I've had a look at the earth connection , engine to body, but I will loosen it off and give it a clean.
Neg lead to battery is good, cleaned and reconnected when I unwrapped the old girl after her winter hibernation.
I've been through the ingition wiring everything seems ok, but will try Props tip in an earlier thread about running the car in the dark and looking for fireworks.
Condensers (*****) always have a part to play in the problem.
Will post the results when I have tried the suggestions.
Thanks again.
John.
J Elliott

If not done already, check the rotor arm as well. My 71 also had the similar symptoms, run ok then start to miss, then fail. Restarts and repeat.
If the arm has a rivet on the top, suggest you bin it and get a good quality red arm instead.
Jeremy Tickle

Thanks for the reminder Jeremy, I've been intending to order a red rotor arm for some time, I will now set about doing so.
Slight bit of misinformation in my earlier entries, I forgot to say that I have an electronic ignition fitted, a Lumenition Magnetronic MTK003, but it has always had a black rotor arm fitted.
Removed and cleaned the earth lead, engine to body, and will give her a run when the sun comes back into the sky, its raining cats and dogs at the moment.
I had a look at the photograph of your car Jeremy and was amused by your stated condition of 'Good', if thats good mine should be on the scrap heap.
J Elliott

Lumenition Magnetronic

Ahhhh... I seem to recall, the wiring on these are a bit thin and do have the occasional issues

Prop
Prop and the Blackhole Midget

Hi Prop, As the electronic ignition has been in the car for about 8 years it may be due for an upgrade, what make would you recommend.
John.
J Elliott

The battery sounding 'dead' points to an earth strap problem - I had a Fiat Panda that behaved similarly and the earth strap was actually broken but in place. Under braking it parted. Many a Panda caught fire from that problem apparently. The cure was a longer strap!
Nick Nakorn

do you have servo brakes?
servo could have a fault letting air in
Mick - still wiring!!

Which ignition would I recommend... hard to beat a rebuilt lucas with P&C and properly set up to your engine spec

But those "123 tunes" sure seem to do the job, peter burguss sells them and has the rolling road to fully set them up...id drop the dime for at least a chat.

Prop
Prop and the Blackhole Midget

I've been tied up with other things for the past few weeks, so here is an update on my problem.
Ordered, from the dizzy doc, and fitted a red rotor arm, the problem was still there.
Ordered a new earth strap, from mgoc, replaced the existing one, took the car out for a spin this morning and had no problems, although the heavy braking was simulated, ie I pre-planned the braking on a clear stretch of road, so no sudden real time braking.
Hopefully the earth strap was the problem.
But, and it's a big but, after the run the idle was running quite high, nearly 1500, so I decided to check the fuel/air mixture and adjust the idle setting, while doing this I noted that the jet assembley on the base of the rear carb had some up/down movement, this caused a bit of a problem getting the mixture right, I've done temp fix by tapeing it into the correct position.
Has anyone any thoughts about the possibility of this causing the sudden dieing of the engine.
John.

J Elliott

The main thing to do is fix that loose jet assembly situation.
If the jet itself is free to move up and down inside its housing and not actively held upwards by the return spring then the mixture on the carb will be all over the place.
If the whole jet and jet holder assembly has somehow come loose by unscrewing itself then that too obviously would have bad effects on mixture control.

So sort that out and then you have somewhere predictable to continue from.
JB Anderson

Thanks JB, I had another look at the amount of movement, which was about 2 to 3mm. The problem seems to have been the screw holding the retaining bracket of the assembly, was able to apply a little more pressure onto the screw to hold the assembley in the correct position, will keep an eye on it to see if it loosens with vibration. Thanks again, John.
J Elliott

Hi John,

It sounds like you have solved the stalling problem but if it happens again, try another coil.

It is not a common problem but I have had a couple of friends who had engies die when cornering in a particular direction. In both cases it was the coil. "G" force must have moved the internals and caused an unwanted internal earth or open circuit. In your case there is braking "G" force. Unfortunately this does not explain the "dead battery" symptom unless an unwanted earth inside the coil momentarily robbed the current needed for the starter solenoid. A long shot but it is easy to try another coil if the problem returns.

Bob Schapel
R L Schapel

This thread was discussed between 24/04/2015 and 03/06/2015

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