The generator on my 1956 Ford Fairlane (292/Fordomatic) was only putting out 11 volts at idle or when cruising with the lights on. When cruising with no lights on, it would put out about 12.2 volts.
I recently had a shop install an alternator in place of the original generator. At idle I was getting a 13.5 volts reading on the aftermarket voltmeter. On the way home from the shop there were two occasions where I had to stop for a traffic light. Both times with my foot on the brakes, the car started shaking from the motor acting like it was not idling fast enough. I thought the engine was going to stall but didn't. It also felt like I had lost the "boost" on my brakes. The aftermarket voltmeter began to pulse each time - going back and forth from 5 to 14 volts. When driving, everything seems normal.
Is it possible that the installation of the new alternator is putting a little more "load" on the engine and to compensate for this, the carb idle needs to be adjusted (increased)? The carb is a Holley 4160/465 cfm - 4 barrel. If it does, what is the best way to make the needed aljustment? I am not experienced in carb adjustments and the shop that installed the alternator does not work on carburators.