OP doesn't mention what engine.

64 Chrysler FSM says 34-40 degrees for both, 27-32 individually, 413 engine

65 Plymouth FSM says 36-40 degrees for both, 27-31 individually, 273, 426W

69 Dodge FSM says 37-42 degrees for both, 27-32 individually, 340, 383, 428, 440 engine

so it varies a touch depending on the year, but probably not enough to matter. I like to shoot for the center of the range and you really should have an FSM as it talks about how to set it and how to check for dwell variance.

http://www.mymopar.com/index.php?pid=31

If this is a stock motor I do not think it will like 20 initial and how fast the rest comes in can cause issues.

Also do not confuse mid rpm cruise with low load (partial vacuum) and high advance as compared to full RPM and heavy load (no vacuum). Total advance is debatable but in the 32-36 range under load. Cruise will be higher. A hemi typically a little less than a 440.

Should gap the points and check dwell individually. Both need to be in spec. Then total should be higher.

A non emissions hemi in 67 used 12.5Deg initial. Had 15-19 mechanical crank advance by 2800 RPM, and would give 0 degrees vacuum advance up to 9" vacuums in stock configuration. That is a total of about 32 degrees drag racing your buddy on Friday night.

A emission hemi in 68/69 had 0 initial and got 32 degrees mechanical at crank out of distributor at 3100 rpm. Same vacuum curve.

Depending what parts have been mixed you should get the distributor curved to ensure it is doing what you think. You can then play with initial. Vacuum advance for stock can is 0 at 6-9"; 9-15deg at 12" and 16.5-22 degrees at 15" (light load idle)

Your probably getting 40 plus at pretty low rpm which is not doing what a hemi wants. IMHO

Ok, so wanted to say thanks to everyone as I've become more familiar with the dual point setup that I'm trying to install.

The original issue still exists, that with both points in use, the engine stumbles just above idle, to the point that it is not even drivable. As I mentioned, if I isolate EITHER set of points, it runs normally.

At this point I know the following:

1) The advance that exists in the distributor is not an issue. I merely backed the initial off so I have roughly the total that I want.
2) The dwell is not an issue. I have a dwell meter and it is set as it should be.
3) Although I have yet to test it, the condenser doesn't seem to be an issue, as I have tried two new ones with the same result. Also, I think I'm correct in saying that if the condenser was bad, it would act the same for a single set of points as with two sets.

Although, this does act very similar to what happens when a condenser goes bad. I will try to play with that next, but just wanted to post and see if anyone has any other ideas?

I would question the integrity of your coil as blocking either set points changes the dwell and has a direct effect on the coils saturation time That appears to be the only variable IMO

You got it! It was the coil!

I have and MSD Blaster 2 in there. I wondered about it, but with it running ok on one set of points, I couldn't exactly see how that longer saturation time would affect this type of coil, that is designed to deliver more voltage anyway.

Put a $19.99 O'Reilly coil in, and it works fine. BTW, the coil isn't bad. I put the old system back in place, and it runs normal. That coil just doesn't like the saturation time of a dual point system.

I would like to understand why this is the case though, if anyone can explain the electronics...

I certainly learned something on this today!

AWESOME !!!!!

As for explaining it you can Google "dwell effect on ignition coil" or similar term


http://dtec.net.au/Ignition%20Coil%20Dwell%20Calibration.htm

One could also try MSD's tech line but that is likely to be a roll of the dice

yeah a coil can be OK cold but act up when warm but I woulda never thought a dwell AMOUNT issue

Interesting, but when you blocked one set of points which one was it and did you change timing? Or leave alone. For DP approaching firing a cylinder, Point Set A open first but nothing happens because set B is still closed. When B opens the coil fires and this is where timing was set. While B is still open A now closes and starts charging the Coil. Then B closes. Hence point B opens to fires the coil, and Point A closes to charges the coil. They share the load of switching the coil. If you blocked B and ran off the A point, you basically retarded timing. Since you started with 20, the motor may have liked that better. OF course this doesn't really explain why a new coil resolved everything, unless you had some intermittent issue.

On the other hand I guess it may be possible that the coil when charging got to point where it shorted and you lost your voltage charge when the dwell was higher, but doesn't do it with lower dwell. Maybe running on single point after sufficient time that coil would start acting up again.

No, I did not change timing. The same thing happened when I blocked EITHER set of points. Yes, the timing does change with one set of points blocked, but not enough to cause the change, i.e. with both sets of points the car won't run above idle, and either set isolated it runs perfectly fine.