Square-bore vs. spread-bore?

Another great feature that the TQ has & the QJ hasn't: the secondaries bleed off cct.
You can get a condition where at cruise, the sec blades are just cracked open, but not enough to open the AV. The AV then acts as a choke & you get an extremely rich mixture.
Carter cleverly has a vacuum bleed off cct to the AV dashpot, such that once the sec blades crack open, the vac to the dashpot bleeds off, allowing the AV to open & admit air so that the mixture is not overly rich. If you open the sec blades, you will see a small hole on the passenger side throttle bore that is blocked off with the blades closed; this the bleed-off port & should be checked for dirt etc when re-building.