We tried a number of things, but ultimately, it turned out that locating the transducer vertically inside the transom, above the fuel tank level completely fixed the problem. The FF41 accuracy improved to 3 – 5%.
This would not have been possible had we not repowered. When we repowered the boat, we were able to clear out a mess of engine harness wiring that was in the transom for the old motor. This freed up enough space inside the transom for the fuel flow meter transducer to be mounted.