Turned out the extra 17080212 carb I had was a bit worse than anticipated, so I didn't bother with it.
A little while back I grabbed another complete carb from the local swap meet, #17056208. The new carb's air horn was slightly warped, so I tried to flatten it just a little and ended up cracking it slightly in between the primaries.
![Embarrassed :-[](https://cliffshighperformance.com/simplemachinesforum/Smileys/default/embarrassed.gif)
Lesson learned, that's why sanding is recommended... But we did get it flat. Also found the APT screw threads were a bit stripped down at the bottom, but it can still be adjusted some. Throttle shafts are also worn, in general the carb was a lot worse for wear than it looked. I threw it together with leftover bits and pieces I had, figured nothing to lose at that point. Wouldn't you know it, the lean spot stumble I've been fighting disappeared instantly with the new carb, and the A/F ratio is a LOT more consistent than it ever was with the old carb. Just runs better in general. Have some high idle issues I think are related to both the worn shaft area and sticking secondaries.
I left the stock 76 (I think) jets and put the .044 rods in, along with the dark blue APT spring. Managed 18.6 mpg on a 450 mile trip, and still could improve the cruise mix a bit. Haven't made much progress with the secondaries yet, even with a high hanger, small rods, and 3/4 turn on the spring it still bogs out when they open.
Now the problem is I need to either find another one of these carbs, or at least one similar enough that's worth rebuilding correctly.