Hey everyone. I just got a rebuilt Rochester AA carb for my olds 303. Now I wanted to ask how to adjust the main adjustement screws at the base of the carb, neither the rochester nor the olds shop manual show this, just the fast idle adjustement. Something like screwing them all the way in and 1 1/2 turns out (for example) or something like that? Thanks
Usually 1 1/2 turns out is a good place to allow the car to start; actual setting is done by ear and feel! Get the thing to run, set a reasonable idle speed, then start SLOWLY turning the mix screws. Engine needs time to feel the new flow as you turn! Move in and out until you get best smoothness, then do same on other. On a new carb never before adjusted to your car, you wll likely need to repeat everything because the 2 idle screws and the speed screw influence each other...idle speed will likely go up during this, so you dial it back down and repeat mixture adjusting. Once you achieve smmoth idle at right speed, go slightly lean on each mix screw and try to get them to just barely above the point at which leaning down causes a loss of idle quality. Done.
Opposite on Rochester AA. In is lean. These regulate the gas flow, which then goes up and over past a non-adjustable air bleed to get into the airflow...thus it needs some time for the new mix to reach the engine as you turn the screws.