Looking at the '47-51 truck shop manual, they say to set the idle at 400-450 rpm, for both the Carter and Rochester carbs. I confess I set mine by ear.
Kent


1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix