My '65 L-79 took a dump. Went out yesterday- after about 3 miles, it was missing badly, and cutting out. Limped it home. Put a new coil in today- got about 5 miles and the same thing, but it would not run at all, got it towed home. Everything else in the ignition looks good- and it came on all of a sudden, except I just changed a leaking fuel filter, and R&R,d the bulkhead connectors, which looked good. Fuel pump pivot pin looks in place, voltages at the coil, ballast, and points check OK. Bad condensor? Or carb issue? What to do next?
Thanks in advance.

 

It's possible, but generally a bad condensor is either open or shorted and not intermittent.
This is what I would do if it was my car.
There are only two possible problems. You're losing spark or fuel. I would find out which before I replaced any parts. If you change the condensor and it starts and you think you fixed it, you may be someplace you don't want to be when it quits again. I would drive it around my home area or in a safe place to get off the road until it quit again. I would have the heater fan and radio on. If when it quits, the radio or heater fan quit also, I would pull the inboard of the two firewall connector plugs under the master cylinder and clean the pins, particularly the large red wire. If the fan continues to run, but the car won't start (no starter action when you turn the key) I would still try wiggling that connector and try again. If the starter turns with the ignition switch turned, pull a spark plug wire off and hold it near the block while someone turns it over. If you don't have spark, you can go back toward the distributor area and check the connections and points, etc for a problem. If you feel like the condensor might be a problem, take one with you.
If you have spark, you most likely have a fuel problem. An issue I have seen more than once is the pivot pin works out on the fuel pump and you get intermittent fuel supply. One of the guys in our club has a 65 that would die or miss badly after a little driving and then would not start (starter would engage). After extensive troubleshooting, he found that the pin was missing from the fuel pump arm. The car would run for a while, start to miss, then die. It would not start until it sat for 10-20 minutes and then start again and run for another indeterminate distance, sometimes miles. I'll attach a picture of the pin I'm talking about. One of the members here on the forum made a bracket to span both sides of the pin to prevent it because he also had the problem. You can search "corvette forum fuel pump pin" or "is this my fuel pump pin corvette forum" and read about all the people who have had this and why. It's an airtex pump design issue that allows the pin to work it's way out.
First thing, determine if it's fuel or spark causing your problem.
Here's the picture and a pdf of a fix explaining the issue if it's the fuel pump:



Slipped pin and broken fuel pump arm spring.pdf

 

I know you said you checked the ignition but along with all of that advice give the distributor cap a good look for arcing on the inside or damage. I limped 25 miles home from a car show with this problem and next day the car wouldn't start....

A screw holding the rotor had come loose...

 

Wow. Looks like it may have put a small crack in the distributor cap too.

 

I'm not sure if it's always the case but a condenser I fried a few years ago was a complete short - car wouldn't start.

 

The fuel pump pivot pin is in place. The red power wire checks good all the way to the cigarette lighter. The bulkhead connectors looked very good. Cap, rotor, and points looked OK. I got a new condenser, but tried running with the old one first, as a base line- the car barely started, and ran really rough. I put in the new one and it started right up and ran smoothly. I will stay in my area and run it for a good time tomorrow.
Will also put a timing light on a plug wire to see how it is firing.

 

Well, like I said it's probably a bad condenser.😁
I've never had a bad one myself but I hope it fixed your problem. Post back if anything changes

 

I had a relatively new condenser go bad years ago. Back when you could buy Wells brand SBC tune up kits at K-Mart! Symptoms were, it would start, run at idle but no power to move the car.

 

That ain't waterproof, just sayin'.

 

I had these symptoms last summer, suddenly. After two weeks of tune up, timing and carb adjustments, fuel filter, changing plug wires, etc. I decided to pull the valve covers. There it was. A broken valve spring, after 50 years and 90,000 miles one finally went. While I was in there I adjusted others that made a big difference.




'66 427 broken exhaust valve spring

 

Update:
New condensor solved the problem. But, while troubleshooting some seemingly unrelated issues, I discovered the voltage regulator was shot, allowing 16 volts charging rate. Was this a contributor? Maybe.
FWIW, the solid state turn signal flasher got ruined also- it worked fine with the engine off, but wouldn't flash when the engine was running with the 16 volt charging rate.

 

That's prob only the third condensor failure I've seen in my 10 years on here. You'll never know if the bad V/R caused the issue; but I'd guess not.

Its always interesting when the zealots come out and claim they've never had a points failure - I guess technically the condensor doesn't count....except for when it does...