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MG Midget and Sprite Technical - hot coil?

Hopefully a quick and easy question.

I've got my 64 midget 1098 up and running now and am doing the last few jobs before the MOT.

However I have noticed a slight miss fire and have found that the coil is getting very warm quickly.

I have converted the car to negative earth and fitted an alternator, so am wondering if I have the coil wired back to front? which side of the coil should the white and white/black wires go?

Thanks
John


John Collins

Wire from the ignition switch should go to SW, and the wire to the dist (contact breakers) should go to CB.
Trevor-Jessie

John. With a positive ground, the SW went to the ignition switch (-) and the CB (+) went to the contact breakers (points).

When you switched to negative ground, the connections are reversed and the negative terminal, marked SW, goes to the distributor while the positive terminal, marked CB, goes to the input wire from the ignition switch.

Les
Les Bengtson

Like Les says

Bill

Looks really shabby that car John. I wouldn't even dare turn up to spridget 50 with it looking like that.

I'm a member of the NSS (national sarchasm society) you know.
Nick

Hi,

thanks for the input, I've now checked my wiring and I was back to front. All sorted now, but coil still gets very hot to the point where you can't touch it, that can't be right? new coil on order for tomorrow.

Nick, LOL! shabby now, you should have seen it a year or so ago!

John
John Collins

John. Do you have a volt-ohm meter? If so, there is a tech article on my website on ignition system trouble shooting. It is at www.custompistols.com/cars/ under the articles section.

If you can measure the input voltage to the coil, with the ignition switch turned on, or with the engine running, and see what that is, it may be a hint. Some of the later model cars, originally designed to run a "12V Coil for use with external ballast resistor", have been converted over to run full time 12V input. Most of my cars are set up that way because it was recommended when I switched over to the Lucas 45D4 distributor.

If, in the run position, you have 12V going into a coil designed to use a resistance wire or external resistor, it will be running a higher than intended voltage and will run too hot. (They all run hot, by the way. They are a transformer and transformers are always hot to the touch after being in operation for a while.) Thus, the input voltage would be of assistance in determining if there is a problem.

Les
Les Bengtson

John - The coil doesn't care which way it is hooked up. Hooked up backward will not cause it to overheat, although since it is providing the wrong polarity pulse to the spark plugs, it will cause a very slight decrease in the efficiency of the spark plug. Check your dwell or gap of the points - if the gap is excessively small, or the dwell excessively long (different ways to say the same thing) it will cause the coil to overheat. If yo are using the original coil in your 64 Midget, it is doubtful that you have a 6 volt coil as Les suggests, but it is always worth a check. Cheers - Dave

PS. If all else fails, replace the condenser, they can fail and cause all sorts of problems.
David DuBois

John

Have you used the coil from a 1500 because it was newer and shinier?
Dave O'Neill 2

I think Dave is thinking ballasted..?
Nick

Coils generally are hot to the touch and I guess the oil inside them is for cooling.
Daniel Thirteen-Twelve

This thread was discussed between 11/05/2008 and 14/05/2008

MG Midget and Sprite Technical index

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