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I have several coil testers, the last one I got, I picked up this year, (an old Allen). It has a setting to load the coil to heat it up, and watch for failure. I didn't get the instructions for it, nor have I had time to mess with it, although it is on my "to do" list for this winter to figure it out. The coil tester I use is a SUN, which works very well for checking the condition of a coil at a given time, but does NOT have the "warm up the coil feature." A person could try warming up the coil with a heat gun, but I think it would take a long time to heat it the the very inside, from the outside in! I posted some months ago about trying to gather up some coils folks had set aside as "defective", to do a little research as to how they would check out on the coil tester. I offered to pay shipping to me, but, unfortunately received only a couple of replies. (I was not looking for coils to use, sell, or otherwise profit from. I was simply trying to get 8 or 10 used, and possibly defective units to compare against each other.) Another possiblity is to install the coil on a distributor, and run it on the KING distributor machine I have, and wait for it to "act up". That puts it under actual operating conditions, EXCEPT for heat from the radiator blowing back over it. It sure DOES sound like you are having coil problems, as the "backfire" is a typical result of the igntion system shutting down, while gasoline continues to flow through the engine, 'til it's "lit of" by the HOT exhaust system. The other possibilities are a bad igntion switch (which you can easily jumper around, to rule out that possibility), or a bad condensor, RARE in my experience, but it DOES happen. I don't recall the setup you have... as-original 6-Volt, or a 12-Volt conversion? If a 12-Volt conversion, there's always the question of what resistor(s) to run ahead of the coil, to limit primary current to a safe value. With the original 6-Volt coil, adding a "converting resistor" of about 1.6 to 1.8 Ohms, along with the OEM ballast resistor usually works out well. For the "so called" "12-Volt" coils that have been sold for years, Dell always recommended using his "trick current limiting resistor" of .5 Ohms @ 20 Watts, and to eliminate the OEM ballast resistor. Now, it seems, many of the "12-Volt" coils being sold like the HIGHER .8 to 1.8 Ohms of the OEM positive temperature coefficient ballast resistor. It would certainly be GREAT to have a definitive answer as to what resistor each (imported) so-called "12-Volt coil needs... too little resistance causes repeat coil (and perhaps breaker point)failure, and running with too much resistance can cause misfire and/or hard starting. Depending upon what resistor(s) you already have, you could TRY adding DELL'S .5 Ohm resistor to the primary circuit, and see if that fixes the problem, or at least extends running time a bit, which would DEFINITELY point to a bad coil. SO.... All that being said, I certainly could check out your coil, which MAY or MAY NOT prove anything, the trouble is, mailing both ways would cost half as much as a new coil! Just now, before posting this, I looked back, and see you have posted again that you have a Pertronix installed. You are correct, in not using a condensor with this. I see also, you are running a "12-Volt" coil. Are you using ANY resistors ahead of it? Were you having the same "loss of spark" problem BEFORE the Pertronix install? Was this coil installed along with the Pertronix, or was it carried over from use with the breaker points? (ENOUGH rambling... I'm "outa here" 'til sometime tonight.) Bob Email me, if you'd like. bigcoulee@hotmail.com
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