D-Jet Light Stumble, Partial throttle only... Options

[GregAmy]

Here's an interesting one.

1974 2L D-Jet. Tangerine-rebuilt and -adjustable MPS (could prob use professional tuning). TPS replaced 3 or so years ago and properly adjusted (to the best I can with a couple alligator clips and an audible ohmeter). Pertronix electronic points; stock untouched D-jet plate. Injectors are all untouched though I've checked thoroughly as I can for vac leaks, nothing found.

I'm getting a light stumble at cruise, but only at partial throttle. It never DIES, it's just a light misfire for a cylinder or two, seemingly at random, and not constantly. It seems to go away when I floor the throttle (and release that somewhat-less-than 90 poines of fury) and it's under a hard load.

It's initially imperceptible to my passenger (wife) but I can feel it. The longer the cruise goes and the warmer the engines gets, the more prominent the stumble gets - never "bad" - to the point where my passenger (wife) will say "yeah I felt that one" but probably only because she was listening for it.

The car never dies. Starts, runs, idles fine (after getting past the CHT donut hole).

Possibly related: poor fuel economy - low to mid 20s - but I've put that down to not driving it a lot (evaporation) and as noted I've not properly tuned the MPS (giving thought to adding an AFR to the car).

Thoughts? Easy things to check?

As soon as Chris gets the racecar engine done and that project is completed, I'm planning to remove the street car drivetrain and go through it, including replacing intake hoses, lines, seals. Might even get the injectors serviced by Marren. Until then I'm still driving it around...

GA