1500 midget--no spark

Topics related to the engines for the later MG Midget series.

1500 midget--no spark

Postby steveo » Sun May 29, 2011 4:37 pm

Hi Everyone

Just started my midget to warm it up and then drain the oil. While the oil was draining, I thought to myself, 'self--why not finish installing all those new ignition components.' Long story short, with new points, condensor, rotor, cap, wires, and plugs, there is no spark. (Yes, it has an earlier mechanical distributor installed). Following through the diagnostic procedure, there is no spark at the coil lead. I swapped in a good coil from my spitfire. Still no spark.

Any ideas where to look next???

thanks
Steve
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Re: 1500 midget--no spark

Postby hoggie » Sun May 29, 2011 6:32 pm

I'm guessing that your problem most likely involves the breaker points and condenser. You should have 12 volts standing the breaker point arm when the points are open. If you don't, then possibly you may be missing an insulation washer. The condenser attaches to the breaker point arm and will charge up with the 12 volts when the points are open. The abrupt current flow charging the condenser is what produces the spark on the coils secondary winding. The points and the condenser are grounded out when the points close after firing.
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Re: 1500 midget--no spark

Postby Charlie Tolman » Mon May 30, 2011 2:00 am

As suggested in the above note, determine if the points are grounded when they are open. They should not be, and there should be 12 volts at the terminal. There is a special isolation washer that fits between the points spring and the electrical terminal.

There is a remote possibility that the condensor might be shorted. If there is no voltage at the points terminal when they are open, disconnect the condensor lead and re-test.
___________________________
An electrical charge being stored in the condensor (capacitor) does not provide the energy to produce a high voltage in the coil secondary. This energy comes from the magnetic flux stored in the coil core (an inductor), which builds-up when the points are closed. The condensor provides an electrical AC path to ground when the points open, allowing the magnetic flux in the coil to quickly collapse, thereby inducing a high voltage in the coil secondary.

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Re: 1500 midget--no spark

Postby hoggie » Mon May 30, 2011 11:12 am

Thanks for clarifying that Charlie. I was giving the condenser too much credit for the spark. I think it may extend the spark period somewhat, but it's primary function is to protect the points.
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