I think I inadvertendly changed it while 'customizing' the gauge. This fuel level sender is designed to work in vented tanks with depths greater than 6-1/2 inches. It is a new type of floatless fuel sender from Classic Instruments. There is no calibration available and settings should not have to be changed. There is a new alternative now available that you might consider if you are still in the process of selecting a gauge set. I switched it back to US (as per Yamaha tech support) and it functions perfect now. It was set to Yamaha which would only show half full. My gauge has 3 settings US, Euro, and Yamaha. Connect the wires on the sender to a multimeter. To test the sender: Disconnect the two wires on top of the sender. You can either test the gauge or the sender to find this out. Anyway both work great and shouldn't require any calibration of the gauge, however, somewhere along the line, my gauge setting had been changed and I had to change it back. The sender and gauge must have the same resistance values or the gauge will read incorrectly.

A close up view of the circuit board shows a series of magnetic reed switches and resistors. The picture above shows what is inside the stainless steel tube on the sender. The OEM required a follow up phone call after not receiving it for a week, to which the guy said he could get it out that day (they obviously hadn't bothered to fill the order til I busted their chops). Taking the sender apart was surprisingly easy, just pop off the metal clip on top of the sender and then pry up the rubber cap around the wiring harness. Mounting Method: 1.5 NPT, American pipe thread, male, 240 30. Material: 316 Type Stainless Steel and operate on a vertical plane (no float arm). If you don't see your required size, click on the down arrow next to the closest size to your requirement. The complete unit was the same price as just the insert (before the 30% off!), and was shipped same day, received much quicker. S3U & S5U sending unit lengths are measured from the top of the threads to probe tip.

I also ordered the Aux tank sender (complete unit) from WEMA. It was just the inside resistor, did not require taking out the sender. I had to change out my main tank sender, did so with the OEM unit, purchased from CT. I can't specifically speak to your year and model, but can tell you about my sender fix: '06 33 express.

Wema fuel senders