This: I think you probably added too much restraint by moving the heavy-spring engagement point. I would've tried cleaning up the low-RPM timing bounce with a slight tightening of the light spring, and set the heavy spring such that it serves to slow the advance rate way down at high RPM.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Hmmmm. Could be. I didn't move it very far, and the weights did pull all the way to the ends of the slots with firm traction by hand

I'll have to continue to play with it.


On the original subject of this thread, I took it out today, in 80-85° F temperatures, for about a 20 mile run, some 65 mph, some 40, some stop and go, and the needle hovered between the "Warm" line and about two needle-widths above it.
The radiator hose became appropriately hard, too.

So the cooling system seems to be behaving.


After playing with the distributor and obtaining a steady timing mark at idle, I set the timing to 5°B.
No pinging.
So, 10 miles into my drive, I stopped and advanced it to 7.5°.
Still no pinging.

So, regardless of the behavior of my centrifugal advance, it is manageable.


BUT, a slight problem from before is now a new, and larger problem.
Last week, it stalled a few times at stop signs when fully warmed up.
Now , once warm, it's stalling sometimes even with brief pauses, then restarting instantly, but being boggy and sluggish, occasionally small-backfiring through the carburetor, and not "blowing out," after opening the throttle, like it would if it were flooded or "loaded up."
Near the end it would cruise along fine, but acceleration was damped.

It's hard to hear the engine while it's doing this, as it's so damned quiet, so I can't go by sound.

My feeling, since it's so smooth and fine at low power, is it's the coil.
The PO had recently replaced the coil with some sort of a fancy hot-rod coil that's bright red, and the wrong resistance (about 0.8Ω, if I recall, rather than about 1.5Ω), and that would be just the part to fail prematurely in order to drive me nuts.
So I've ordered a new Blue Streak coil of the proper resistance, and we'll see if that cures it.

I've got work the next couple of days, so no playing, but I've got some CV grease coming, to do the universals, including that overgrown steering column joint behind the transmission, and I've got some decent shocks coming (sadly, Bilstein doesn't make anything to fit this series), so that should make things a bit better, too.

'Till later,

– Eric

Update:

Replaced 1-2 year old Edelbrock MAX*FIRE 12 Volt Performance Ignition Coil, #22739 with a Blue Streak coil.

It's 10°F cooler today than a couple of days ago when the car had stalling problems, but I warmed it up, let it sit a bit (gauge barely went down), then warmed it up again and drove it several miles, and no stalling problems. The coil was plenty hot.
Idle also seemed more steady, and seemed happy at 450 RPM in Drive (I didn't leave it there – why tempt fate?).
Also had good power throughout the range.

Note: The "Lifespan: 1 year" Edelbrock coil is $50 on Amazon, and I bought the Blue Streak coil for $25 plus $7 shipping from RockAuto.

Centrifugal advance was still a bit shy of 23°, was maybe 18-20°, so I'll have to sort that out.
I can get my mitts on a distributor machine, which may or may not work, and may or may not be compatible, so I'll try it with that if I can.

Temperature gauge needle stayed on the Warm mark the whole time, so I think the original point of this thread has been exhausted.

– Eric

Update: Nearly 100°F here today.

Went for a roughly ten mile drive. Temperature gauge settled in just above halfway and seemed to be steady there.

Timing still around 7-1/2°, no pinging at all. I'll probably adjust it closer to 10° when it's not blowing 200°F air into my face.

I got a set of springs, along with a nifty hand-drawn advance graph, from Slant6Fan, and may have access to a distributor machine next week, so we'll see if I can get it tuned to where it should be.

– Eric

In keeping with the general "cooling system" theme, does anyone have an opinion on using the '60s through '80s Mercedes-Benz cooling fan and fan clutch?

I have the part numbers (though not with me), and both are available new for a fair price.
I do not have a MB graveyard near me.

I've had one Mercedes (1961 190b) and was always impressed with the design and build quality of their stuff, so using their parts seems like it could be an actual improvement.
To my mind, swapping a 1930s-era fan design for a 1960s-era design would be unlikely to not be an improvement, and that fixed fan just seems so... primitive.

Also, in the very hot weather, the Dart's engine definitely heated up some when not moving, and took a while to shed that extra heat while moving, so a fan improvement would seem reasonable.

Also also, I clearly recall, back in the days of my youth, that cars used to overheat a lot more than they do now. In fact, in the 1960s, on a hot day, you were guaranteed to see at least one on the side of the highway anywhere you went, and these were not just broken-down junkers.
So, based on nothing more empiric than my memory, I would suggest that many, if not most, '60s cars had cooling systems with a thinner margin of comfort than is now the standard. (It seems you can leave a modern car idling for hours with the A/C on in the sun on a summer day without a second thought. Nobody would have been mad enough to try this back in the '60s).

- Eric

Yes: yes, or a similar Toyota item. See here and here.
There are many part numbers—many different fan blades with different diameters, blade counts, etc.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.