I had to replace the accelerator pump in my TQ with one that is more ethanol friendly because the old leather pump material contracted enough to not get a proper squirt.
It looks like you are missing something, but yes that is what turns to put tension on the spring. I'm not sure if it changed over the years but here is a pic from my avs off a 68 340.
Sorry, I've been digging through my old books and all I can find is a diagram and instructions how to adjust the linkage. You got me interested now because my 62 Newport has similar linkage. I'll keep looking.
My bet is on the thermoquad rebuild someone forgot a well seal o-ring, they are easy to overlook. Mine was leaking bad and I replaced a bad o-ring, now it runs like a champ.
Ninja edit-- x2 on everything RustyRatRod said