This is one of those things about the Slant-6 that sometimes refuses to comport with common sense. See if adjusting the distributor clocking by 1 tooth changes things for you.
The Slant-6 EGR system uses venturi vacuum to trigger a vacuum relay (a hockey puck-lookin' thing Chrysler called a "vacuum amplifier"). Venturi vacuum is nowhere near strong enough to operate the EGR valve, but it is a good signal of the relevant aspects of engine load for EGR operation. When the venturi vacuum reaches a certain level, it causes the "amplifier" to send manifold vacuum to the EGR valve — unless other aspects of the EGR control system, such as the coolant temperature sensor(s) or the holdoff timer or other widgets (depending on year and model) prevent vacuum reaching the valve.

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

Huh. I'll re-clock it when I get home, I guess. This car was little more than a wreck in a field when I got it, and the entire EGR system was disconnected. Come to think of it, I think the only intact 225 EGR system I've seen was on a '76 Aspen parts car i had for my Duster. I still have the timers, though. I was removing them when I got the thing home and forgot that chryslers were still using externally regulated alternators in the mid-seventies; took the regulator as well and then wondered why it didn't charge!

One tooth back was usable, but took up all the adjustment I had on both slides. One forward was far too advanced to even start, again with all the adjustment taken up. Also did a running compression test, 50psi across the board. The inductive clamp I got is worthless; won't pick up a damn thing.

Alright, might have a clue here. Took it out for a drive today - with the vacuum advance hooked up - and while I could tell it was missing occasionally, it wasn't near as bad under load. It was doing just fine until I pulled into the driveway, when it stalled. Popped the hood to see gas POURING out of the carb. I mean, intake and exhaust soaked, puddle in the divot on the intake and probably 3/4" of gas sitting on top of the throttle blades. Guess I'm ordering a new needle/seat and float and we'll see where that gets me. Maybe that's been the whole problem, though I've never seen drips from the mains until today.



I did manage to get a working clamp for the scope, but only for the ignition wires. Didn't get a picture of it running but the ol' Tektronix 1117.5 (rest in peace trace 2) showed a consistent pulse from each wire.

The floats usually don't make problems, but sure, if you can easily find one. Needle/seat, yes. Crudely "remanufactured" carburetors such as this one in your pic, much bigger yes.

Float height setting is crucial. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

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