Bad Condenser Symptoms?

[Wilbur]

Ok. Here's where l am. Decided to try to start it up. Installed new plugs, put the same cap and rotor parts back, turned the gas on and cranked her over. No start. Pulled the coil wire off the cap. Cranked it over, key on, and had no spark. Key off, checked for 6 volts at both coil terminals. Good. Removed cap and rotor, turned the key on, put the coil wire near a ground and manually opened closed the points to trigger a spark out of the coil. A quiet arc occurred at the points and, maybe one in 8 times, l got a high voltage spark out of the coil wire to ground. So, whats bad there... coil or condenser? Can anyone explain to me what the condenser does?

[MikeK]

Originally Posted by Wilbur

. . . Can anyone explain to me what the condenser does?

The ignition coil is a high ratio transformer. Transformers do not work on straight DC. The magnetic field must be moving to induce electrons to move in the windings.

When the points open the ignition coil magnetic field collapses (moves) and induces an electro-motive force (voltage) in the primary as well as the secondary coil. It's not very much in the primary coil because there are only a few windings in the primary, but it's enough, maybe up to 200V, to jump a small air-gap such as the one between the barely open points. That tiny spark is enough to erode metal away from the points and you'll burn up the points in a matter of minutes. The condenser (capacitor) is an electron reservoir and prevents the points from arcing by absorbing the induced primary voltage rather than letting it arc wildly across the open points.

If you have a solid state (transistor) switch instead of mechanical points there is no air-gap to ionize and maintain an arc, so no condenser is necessary. Example: Pertronix "ignitor" modification. Of course, that mod has it's own set of problems!

[Wilbur]

Mike, thank you for the explanation. Given the details, what's your opinion of my issue? Is my coil done for?

[Duffy1]

I bought the same dist you bought from the same vendor . Installed the dist . car would not start took dist out and apart found incoming wire touching housing . Moved wire off of housing put dist in car and started her up . Car ran for about and hour and then had the symptoms you describe. Lets see new dist ,points , cond . so can not be these three items so was thinking about working on the carb then I rembered what I had read on FB that 95% of carb . problems were electrical so I thought the situation and decided to change out the condenser . Problem solved . Also replaced the point with more robust points from NAPA . So I wonder if these dist are not tested prior to sales .

[Karl]

Faulty ignition switch can cause exactly the same problems you are describing Karl

[MikeK]

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Originally Posted by Wilbur

Mike, thank you for the explanation. Given the details, what's your opinion of my issue? Is my coil done for?

All of the possibilities the fellas have suggested are plausible, and that makes it kinda fun, like playing "Clue". When it gets too drawn out, like a monopoly game stalemate (3 days!!) the fun dwindles.

I'm not one to react like a modern car pseudo-mechanic and suggest you just start replacing parts 'till you win, but a condenser is a part that is difficult to check under actual working voltage, engine heat, and frequency conditions. It is cheap and easy to swap out, so I'd start there. A meter test will tell the static capacitance and DC leakage, but that can be deceiving. If it is not the condenser, that's OK, it's always nice to have a known-good one in your trick bag of Model A tidbits. Go from there.

A coil is also difficult to test under heat and working conditions for internal insulation break-down and partial winding shorts. It is EXPENSIVE, so I'd run down everything else suggested in the replies first, unless you have a dizzy test machine or you're Rockefeller or have a bucket full of spare Model A coils, one of which may be good.

It was Professor Plum in the library with the candlestick. Do I win or am I out?