[Bruce Edwards]

Most older cars will not charge at idle. The alt is just not strong enough. If you are running the coolest plugs for your model you may want to start in the middle of the heat range and adjust from that point.
Installing a smaller pulley on your alt will get it to charge more at idle but in real time how much idle time will the car see? If you make it to small the other problem is the alt turns to fast and sometimes they will fail due to the high internal speeds. The Ford Mustang Cobra came with a very large alt pulley to slow it down so it would not have that problem at high speed.
I would stop playing with it till you can get some road time. Things will be different on the road than in the garage.
How close are you to road time?