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MG Midget and Sprite Technical - hiccups

The car has hiccups every 10-20 minutes. There is no power for less than half a second. No bang afterwards. It only happens at half throttle, not at full throttle. What can I do to find what it is? (1275, 123 ignition, HS2 carb)

Flip
Flip Brühl

When it happens, look to see if anything shows on the rev counter and next time after that try pulling the choke out to see what happens.

By loss of power do you mean like a total flick of a switch type of loss as if an electrical connection has failed, or total engine shut down. Or engine continues to run but no engine power?

My initial thoughts are, perhaps some electrical loss like coil or king lead or their connections or other electrical connection, wire, ect., or perhaps some petrol/carb(s) sticking/fowling (accelerator pedal connections or cable?). (hicupping perhaps kangerooing?)
Nigel Atkins

Does it still have the mechanical Rev counter?
Dave O'Neill 2

Flip, do you have a red rotor arm fitted?
Jeremy MkIII

Thank you for your suggestions:
The electrical rev counter works well during the hiccups So the electrics from the ignition to the rev counter is ok or the hiccups is to short to influence the rev counter.
I have a brown Bosch rotor arm that I trust well.
Yess the car is kangarooing during the hiccups.
I will control all the electrical connections to the ignition.

Flip
Flip Brühl

Flip,
I've found with my 123 the posts inside the dissy cap can be quite scared so a quick clean up once a year plus a clean of the rotor tip.

123 rotors are usually Bosch, or perhaps replaced with Beru, but both are normally good quality unlike the piss-poor Lucas ones. The generic "red" rotors from other than Distribution Doctor are much lighter and not as well finished as the Bosch or Beru but I think work well (but look like they may not last as long).

I still wonder about king HT lead or coil or their connections as the delay between hiccups may be something to do with items, or the environment they're in, be affected by things warming up (or I might be totally barking up the wrong tree).

With connections I'd also be checking earths, even dissy tight to engine although that'd suggest more vibrations and bumps in road than regular time interval but sometimes these issues can be a number of small faults getting together for greater diagnostic fun.
Nigel Atkins

Nigel's reference to the rev counter is that if it flickers it can indicate a fault with the low tension side of the ignition circuit. But only of course if its an electronic, not a mechanical one. And it won't respond to a fault with HT side of things - plugs or leads.

If the car otherwise runs OK and the hiccup is that infrequent, or slight, I wonder if it is picking up droplets of water from a contaminated fuel supply. At full throttle it may just blast past the moment, as it were, but possibly be more obvious at mid range revs. Maybe clean the fuel filter, if you have one fitted. (I don't, for UK fuel)

If your fuel tank is one with a drain plug, you could try letting a litre or so out at the bottom. With the car still for a while before you drain it, any water would find its way to the bottom of the tank and should flush out with the first bit to drain, so you shouldn't need to drain very much to clear it.
GuyW

Have you checked your plug gaps lately
If it's only on part throttle cruise as you describe it could be a lean burn missfire which can be caused by the plug gaps being too wide for the spark available to ignite the lean mixture
Try the gaps at .025" and see what happens

Not saying this is what it is but a possible ---worth a try
William Revit

One of the clamps of the distributor cap was not connected. I ll see tomorrow if that was all.

Flip
Flip Brühl

It is over so far. Thank you all.
Flip
Flip Brühl

That's great.

I would have thought (but I'm very often wrong) the clamp being off would have caused a more frequent problem if it caused any.

As it's a 123 is it the top or bottom clamp that was off?

As it's been suggested that the 123 clamps could loose although I've not found this but I can slightly turn the dissy cap with the clamps fitted but not enough to be or cause any problems.
Nigel Atkins

My 123 dizzy cap clamp springs seem to slacken and loose their clamping force over time.
After 2000 miles last year they were only just holding the cap on. Its easily rectified by bending the springs back to shape, but its annoying on an expensive bit of kit.
Chris Madge

This thread was discussed between 01/03/2020 and 04/03/2020

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