When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
From: At my Bar drinking and wrenching in Lafayette Colorado
There are no air mixture screws on a Rochester carb. The idle mixture screws control fuel only. The screws are size 10-32.
However, I have a feeling that you do not want to know what size the screws are. I think you're actually asking about the drive head configuration of the screws, which has nothing to do with the screw size. The 1979 Q-Jet idle mixture screws utilize a tamper-resistant head design that measures .175" x .220". Adjustment of the screws requires use of a special idle mixture screw adjustment tool available from most auto parts stores. If your carb has not been messed with and is unmolested, these screws will be installed behind protective steel caps which must be removed in order to access the idle mixture screws. If the steel caps are gone, and if the screws look different from the ones shown below, your carb has been altered and messed with, and you may have a real can of worms on your hands...
