Hi, I use they carbs also,they work quite well,better throttle response and even better fuel mileage.The stock main jet is usually a #65,they are the same jets commonly used in Holley 4 bbls.
Another factor is the power valve jet restriction,they vary widely depending on the original application for the carb. Carbs from truck models have a power valve jets that generally are .010-.020 larger than the passenger car model.
If you engine responds cleanly at part throttle when fully warmed up,the main jet is ok,or you can jet down a size or two and try it out.
If you feel the engine is rich or lean at full throttle,you can fuss with the main jet, but better results come from changing the power valve restriction.
If you are comfortable working on carbs, remove the metering block assembly from the float bowl.At the one end is the spring loaded power valve jet restriction.You have to remove several plugs by carefully pulling out the plugs,spring and valve to expose the jet restriction.The jet isn't easily removable,so to enlarge it use proper size pin drills.To decrease the size,use a small length od fine wire in the hole or swap out the metering block.Press the plugs back in using a small dap of epoxy to seal the plugs.
