As previously mentioned, try bumping the initial timing to 18 degrees. Then with the engine at running temp (after a short drive), leave the car in D and apply the emergency brake. Then hook your vacuum gage up to the intake (manifold vacuum)and write down your baseline vacuum reading. Then start with one of the metering screws and turn it in 1/8 turn and watch the gage for 20 seconds or so. If the reading produced more vacuum, then go to the next metering screw and turn that one the same amount and the same direction. If the vacuum got worse, then turn the screw back to where it was and then another 1/8 turn in the opposite direction. Do this with both metering screws (back and forth) a few times and then take note of the vacuum reading. Then readjust your in gear rpms to where you want them and take note again of the reading.
You will want to accomplish the in gear idle rpm desired along with the highest in gear vacuum reading along with the steadiest vacuum reading while in gear.
Note: Before this test, make sure both (or all four) metering screws are currently set at the same amount of turns outward. It helps me to make a mark at the 12:00 position on the metering screws once I know that they are all at the same position. Then after I am done tuning, I can reference all of the metering screws to see how far they had to be turned.