Engine Run-On: 400 Tri-Power
Do a search on this website on tuning a 400 with tri-power. It will tell you what carburetors that you are suppose to use. The center carburetor has the idle circuit and choke. The other two do not have an idle circuit and choke. The outer 2 carbs are on a progressive linkage so they are only used during 3/4 to wide open throttle.