[HotWheelsFan]

There are many aspects to carb air/fuel metering. You may have a correct or "smog worthy" jet size, however the power valve piston spring may be incorrect for the proper A/F mixture. This can cause an improper A/F mixture due to the vacuum required to lift the power valve needle when needed. Power valve rods also have different calibrations as well.

Carb calibration can be tricky with out a dyno as many factors are influences of the fuel metering system.

In response to the jet sizes I use, or am familiar with of hand, are 70 -72's. That's not to say that they are correct for my applications, they just seem to common ones I have used in the past.


Bob

PS - I rarely use stock model or year correct carbs as most Chevy parts interchange. I also try and use later model carbs to avoid worn carbs from the late 60's era. This will affect jet sizes as I may use, or have seen common in my carbs. There's a Rochester Carburetor book out that may help with tuning and understanding how the Quadrajet meters fuel delivery under the range of uses, and carb fuel delivery circuits involved.