There are some differences in the carbs. The newer ones use a single vacuum diaphram on the choke pull off and the older carbs have two. It doesn't make any difference if you swap carbs, but it means you can't just swap individual parts. Sounds like that is the part we are talking about. If the diaphrams are leaking, you'd have a vac leak on top of the choke not working quite right. I managed to run my 76 with one of them plugged off and it didn't really make much difference, but I don't quite know how the two of them work together. Could be the 79 with only one would run like crap if it isn't working.
Solution? I dunno. Check the short bit of hose on the carb for a leak, and try plugging it off and see if it helps/hurts. You might be able to swap the whole works off the 76 carb and get it hooked up, I'm not sure what else would have to swap with it. If your 76 carb is in good shape, try swapping the whole thing and see what happens. If all else fails, get a weber.

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)
MEPR: Man, my 4x4 makes all other LUVs look good
