What is the actual difference between merc carb 1389-9564 which is used on pre 1983 3 liter (140 hp)and 3.7 liter (165 hp) and the 1389-9350 which is used on 1984 and up to 2001 140 3 liter engines?
One difference is the linkage design and the other is the fuel pump overflow tube. Also there's a possibility that the Venturi Cluster or jet sizes are a little different. Some of the jets were between 1.45 up to 1.65mm looking in the service manuals, etc.
http://flyingfishcarburetors.com/Y38-4AMercruiser.htm
http://flyingfishcarburetors.com/Y38-2Mercruiser.htm