Ok, so it hasn't been all that cold yet, but I just reinstalled an old faithful Quadrajet I've owned since the 1980's. Years ago, I chopped the choke off, because I have no heat going through the intake to run it anyway. I started the car tonight and it actually idled cold (at about 450 - 500 rpm)! This is with No choke and No heat. It was probably low 70's or high 60's outside. I'll b interestd to see how it does in the low 50 degree weather! Yeah, it was on the verge of stalling, but it didn't, and I have a theory why. At such low rpm, the engine vacuum isn't very strong. I'd bet that my stock power piston is opening, letting a richer mixture through - richening the mix enough to somewhat compensate for the lack of a choke. When the car is warm, I have nearly 15" of vacuum, so I'd assume that the stock power piston (valve) works fine then. Kinda neat that the poor-cold-idle might just me helping the car from stalling when cold! Any thoughts?
it looks to me like power piston feeds the fuel through the primary venturi. With the throttle plates closed at idle there won't be vacuum at the the primary venturi so there shouldn't be any fuel coming from there.
I see what you're saying, but... Carburetor books always stated (as far as I remember) that low idle vacuum will open the power circuit and destroy idle quality, even to the point of making the engine eventially stall. I believe that the valve will open and the fuel will get through - that seems to be the general consensus.
