You do not really need the fuel sensor kit. I bought the speedo combo and installed it without the kit. The idiot light on the speedo comes on just the same as with the original speedo. Then later, I bought the sensor kit and with that new sensor kit my fuel light is a bit more accurate when it comes on. Before the new install, the low fuel indicator light would come on with only 125-135 miles on that fuel up. I would think that I only had about .75 to 1.0 gallons left in the 4.5 gallon tank. But I would only be able to put 2.7 to 3.1 gallons in to make it full. A couple times I carried an extra gallon with me and would ride until I ran out and would get 180 to 195 miles on that tank. Now the idiot light comes on at about 155 to 160 miles. You will never be able to get the full 4.5 gallons of fuel in the tank because the pump and filter take up that extra space in the tank. That tank if on a gravity fed carb would indeed get a full 4.5 gallons. A couple things I like about having the sensor kit installed is the speedo is more like a toy. I can see approximately how many miles left until empty, and also the fuel level bars give you at a glance approximately how much fuel you have remaining. Before I used to always trip my meter and watch the miles driven on that tank to estimate when to stop for fuel.