In my 1972 Dodge Coronet Custom with a 318, I wired the heat riser valve open a couple years ago due to incessant rattling. That was during a Kansas summer and, looking back, the following winter may have been the beginning of a lot of lean stalls during cold startup. The choke closes the butterfly valve prior to startup as it should, but during startup the choke valve opens too much--thus the lean stalls.

I just came up with a theory that the choke operates fine because it closes when the it's cold and the throttle is opened, the choke pull-off operates fine because if it failed it would pull too little (not too much), and the freer flow of exhaust (due to heat riser valve wired open) is causing extra vacuum at the carb, thereby pulling the choke pull-off too much. The pull-off would have been calibrated to work with one exhuast pipe obstructed and therefore less vacuum pressure.

Does this make any logical sense? I'm about to free up the heat riser valve and see about fixing the rattle, and let it operate as it is supposed to. The anti-rattle spring is in place and I can't see anything wrong with it, incidentally.