[greg0380]

maybe this helps. Before switching to TBI I messed with my 85 qjet alot. On the bench I was able to set it up and it worked great (for a while). There are steps on the fast idle cam that work in conjunction with the choke blade angle. The idea is that a cold engine requires a richer mixture. The carb does this by increasing the throttle angle to give a higher engine speed when cold. This is why you have to pump the pedal once before starting, the choke is able to close and set the idle screw on the fast idle cam. the choke blade on top acts like a restriction in the intake path. The increased engine speed pulls in more air and the choke blade that is almost closed restricts the air but causes it to flow faster. This air moving faster past the main venturis in the carb (which normallly are not used at idle speeds) now with the increased velocity of the air will start to siphon a little bit of fuel from them. This is what richens the mixture for a cold operation. THen as the choke warms and opens towards fully open the fast idle cam falls to a lower notch until it is completely riding on the normal idle cam.

When the engine is cold the fuel doesn't atomize well in the intake manifold so fuel tends to condense on the cold metal and never makes it into the combustion chamber. Richening up the mixture compensates for this until the intake manifold is warmed up and the fuel stays atomized after leaving the carb all the way to the combustion chamber.