I use a .22 MFD (double check your condenser's specs.) CAPACITOR from a electronics supply. Much more robust than the junk condensers that are only manufactured as an obsolete  afterthought now.



"FREE SAMPLE"

I had a similar experience, same symptoms. When cold all was well, when hot all was hell, backfiring on steroids. I was 12v with new resister and condenser. Long story short the ballast resistor was replaced with and old one and the car ran fine for a couple hundred miles when the miss and backfiring began again, this time it was the condenser. I was now in Memphis, Tennessee and drove back to NY with no further incident. I’m now all electronic ignition and my blood pressure has returned to normal.

1955 312 T-Bird Warwick, NY

I am definitely not an expert in this area, I had the same issue back in the day running dirt track, I had 12 volts going to the points and they didnt last long I was advised to put a resistor that brought the voltage down to 6 volts to the points and that fixed it. 

I don't know if it's the voltage so much as the current (heat) that is the issue here. Maybe arcing becomes a factor, I don't know. Excessive heat will cause coil trouble. He mentioned replacing with an "internal resistance" coil, but the details matter. I assumed it was a standard ignition points coil of approx. 1.5 ohm primary winding. Coupled with the ign RUN ballast of approx. 1.5 ohms, this will keep the total ampere flow through the ignition system within spec with the engine running.

It's probably a good idea to check "point resistance", between battery negative post and the movable points plate in the distributor. Depending on the distributor design various intermittent ground defects can cause trouble, too. Frayed primary wiring from coil to distributor, or the bare copper stranded strap that grounds the points plate to the distributor housing might be missing or "not installed".

Which one do you use? I have several in my kit for radio & stereo work. I tested some Sprague "Orange Drop" 715, these are large 600 volt 0.22uF film capacitors. The thin metalized film type are said not to work in this application. The orange drops seem to look great on a scope in the garage but I didn't try them on a road trip or anything like that. They have solid leads though, so they would need protection from vibration or they will work harden and break, I expect.

I know what you mean about blood pressure! :-D When I was on the roadside dealing with this I was really reconsidering going with Pertronix.  I still might eventually make that switch.

I just did a quick check and found the following, with drivetrain cold and ambient temperature of about 55*F:  coil primary resistance = 3.0 ohms, secondary resistance = 9560 ohms, voltage drop from coil negative to battery negative, 0.145V (key on points closed).  My distributor, points, and condenser are 1959-spec.  The coil internal resistance is very close to the '59 cumulative resistance of ballast + coil, the range of which is 2.7-2.94 ohms per the factory service manual.  The '59 stock coil is supposed to have 8000-8800 ohms secondary resistance, so my current coil exceeds that.  The manual also expects a coil negative to ground voltage drop not exceeding 0.1V.

I'll also note that the distributor was disassembled and thoroughly cleaned before installation just a couple of hundred miles ago, and that the breaker plate ground wire was replaced at that time as well as the coil to distributor terminal wire.  The only piece of primary wiring I haven't replaced yet is the distributor terminal to points terminal wire, but it hasn't shown any voltage drop any time I have checked it.  If trouble persists without an obvious culprit, I will replace it.

My current plan is to keep driving and just periodically check the coil to ground voltage drop for signs that it is increasing.  I will of course have diagnostic tools and spare parts on hand!  Do you think the differences in coil spec would have significant impacts on point life or ignition performance?



1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Back in the day, we never worried about these things.  We ran down to the local auto parts store, bought new points and a condenser and rode down the road. These days, buying points and condenser for a Y-Block is like playing a slot machine with a 50% house edge.  Buy a Pertronix unit and the matching Pertronix coil and forget about it.  My TBird engine starts first time every time and never misfires, stalls or leaves me on the side of the road.  I do miss waiting around for the AAA tow truck driver.....    :>

There is a guy (Jon G) on www.stovebolt.com which is old GM trucks that developed a capacitor that replace condensors in most any situation. Fits in just about any distributor or can be mounted externally. Search the Forum section for "The electrical bay" section and browse for "Aftermarket condenser". Looks to be a pretty good idea.

SE Wis

The points to me look like too high of a voltage but they were not blue like others I have seen not running a ballast resistor. I suffered twice with point/condenser problems before going electronic. Many to choose from and I haven’t changed or had to clean spark plugs for 8 years. Timing also never moves. 

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Honestly I can't see anything wrong with those point faces in the picture?

I ran points for a long time, thousands of miles and they always looked something like that. Like somebody mentioned, nobody paid any attention to this stuff years ago. We just drove.