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MG Midget and Sprite Technical - Odd starting issue

Had an unusual issue yesterday when I was doing my monthly 'run the car for 20 minutes' routine.
Usually, it's choke out, turn it over for a few seconds and it fires straightaway. Yesterday however, it turned over for quite a while then didn't kick until I released the key. Tried again - same thing. Third time, when I released the key it fired up after the kick.
After I'd let it run for while to warm through I switched off then tried to start it again. Turned over but didn't kick/fire until I released the key.
This seems to be slightly odd behaviour so I'm wondering if it might be a symptom of the Accuspark module about to give up the ghost? It's the second one I've had - the first was faulty and packed up within a few months of getting the car back on the road in 2013. This one has behaved faultlessly since.

Graeme
graeme jackson

First thing that springs to my mind is a problem with the ignition switch or wiring, so that when the engine is being cranked you aren't getting power to the ignition (white) circuit.

Then we you release the key to the "on" position, power is restored to the ignition and the rotational moment of the engine is just enough for it to start.
Malcolm

Does it have a ballast coil system? Or is that only on the 1500 cars?
GuyW

Malcolm - I'll check the switch.

Guy. No it doesn't
graeme jackson

Graeme,
we've had a couple of ignition switch threads recent so further details will be in them.

As a first and easy try, disconnect the battery, (you can leave the switch connections as they are), spray the back of the ignition switch with an electrical contact cleaner whilst turning the ignition key to get the switch through it's full range of movement so contacts at least once. Leave a while to 'dry out', then if you if have any a quick and light spray of something like Servisol Super 10 switch and contact lubricant and leave a while before reconnecting battery.

If you enjoy such things as contortion over the driver's seat and in footwell you could try removing the switch from the lock but it wont gain you more access to the switch than leaving it in situ.

If it works great if it doesn't you lost very little but time and materials (even less time and risk of damage to yourself or car if you leave the switch in situ).
Nigel Atkins

Graeme
Is the battery a bit low? With starter engaged, battery voltage is pulled down then, when key is release, goes up again. Battery terminals clean and tight?
Bill Bretherton

Graeme. It is not likely to be either the ignition switch, nor the factory wiring. Bill has a good point about low battery voltage if the battery is getting older and/or the starter is drawing more current than normal. With a points type system you should still get spark but, perhaps, your aftermarket points replacement system needs a higher current output to fire the coil than your battery is capable of providing right now. Thus, cleaning the terminals, the battery clamps, then charging up the battery until it shows fully charged would be a good first step.

Second, if you can recruit an assistant and you have a timing light, hook the timing light up to the high tension system and have your assistant crank over the engine. If you show a weak, erratic spark when cranking and, as the switch is moved to the run position, you get a strong spark and the car starts, you that your problem is either the battery or the ignition module. Battery can be removed and tested under load. I do not know anyone who tests out the aftermarket points replacement systems and, as the factory advises for testing the coil, "replace with a known good unit".

Les
Les Bengtson

If the ignition is a replacement part from the last 20 years of manufacture then it could be suspect - or if it's original or very old then just worn.

Always, always you want your battery and all connections and earths in good condition and the battery at a good rate of charge.
Nigel Atkins

I'm sure years back someone suggested a reason for this starting as you let go but when I put this up on the B section recently, before this thread, I didn't get that answer and have no idea how to phrase an Archive search to get what I want (imagined/misremembered?).

Nigel Atkins

My money is on the ign. switch
Maybe the contacts inside have dirtied up a bit from just sitting around
I was going to suggest the ign. points are too close/dirty but then noticed electronic ign. so that's out---although it could still be the module
I'd just quickly flick the ign. switch on-off several times and hope that that cleans it up-
You could attach a test light to the power side of the ign. coil to check consistent power supply with ign. on and while cranking, If you have good power all the time then your module could be looking like being the problem-
William Revit

You could just watch the ignition light and see if it remains lit when the starter is engaged. Or if that's not certain then disconnect the trigger feed at the starter solenoid so the starter doesn't pull current and see if the ignition light stays on when the key is turned fully to the starter on position.
GuyW

Thanks all. Plenty to look at this weekend.
graeme jackson

Hi,
I had a similar issue. Turned out to be the ignition switch exactly as Malcolm describes.
Dave
Dave Brown

This thread was discussed between 15/03/2021 and 18/03/2021

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