Typically the port closest to the block is for the High Altitude Control (HAC) to advance the timing due to lower air pressure. It doesn't do anything below I think 5000 ft. The other port (close to your radiator) is your typical vacuum advance port.
If you have them both connected to a "y" and running into the same port on your carb ( I have a Weber 38 ), will that just advance the timing more?
