The adjustment you're talking about is called the "adjustable part throttle" setting, or just "APT" for short. Using those terms will help you find additional info on the subject should you want it. The setting procedures will all be for a Quadrajet 4-barrel- but they are basically the same for the Rochester Dualjet 2-barrel you have, which is the primary side of a Q-jet carb, anyway.mrdjsweet03 said:i have rebuilt a carb on 79 3.8 firebird someone before me has adjust the metering rob screw does anyone know how many turns it should be
I use the choke or my hand to partially block some of the air into the carb. I set the APT to where there's a slight increase in RPM as I "choke" the carb some, while running @ 2000 RPM. Not so much that it stumbles or tries to stall, just enough to see if- and how- the RPM changes. This indicates I'm just at the lean edge.
Another method (from SMI, IIRC): "simply turn the screw DOWN (CW) 1/2 turn at a time until you experience a "lean surge". (It will feel like someone is moving the throttle, when their not, or a hesitation on light throttle acceleration). Then turn the screw UP, until the lean surge goes away.
If you are experiencing an "off-idle stumble", you can turn the screw up at 1/4-1/2 turn at a time until it is eliminated. But be sure to adjust your idle mixture screws properly first, as they can also cause an off idle stumble.