idle and a couple other things

Two ways to change the idle: One is to use the idle adjuster screw on the carb (behind the lever the throttle rod attaches to) the other is to advance the timing a few degrees. This may need to be done anyway, depending on what the shop set the timing at. If they did the book figure (6*BTDC), you need to advance this to 10-12 degrees, the idle will go up a few hundred rpms with the advanced timing. With an automatic, the idle needs to be as fast as you can get it, while its in gear, but not so fast, you end up getting a sore leg trying to keep the car from rolling with the brakes applied. With a stock converter, this is about 600-700 rpms.

If they changed the intake, the timing had to have been reset. The distributor HAS to come out of the engine before the intake can be removed.

Oh, and do not put a"too stiff" spring on the carb. It only needs to be stiff enough to return it to idle. Too stiff and it'll wear out the throttle shaft bushings in the carb before their time. You can stretch or shorten the single spring to increase or decrease the tension. What carb you going to put on it ?