My brother recently bought a KF Classic IV. While doing taxi tests, it ran for about an hour and a half, then quit. The EIS said Low Fuel Pressure. He loaded it on the trailer and took it home, where it promptly started and ran on the trailer with the wings folded back. He was unable to find any problems. About two weeks later, he was flying with an Instructor, and after about an hour and a hale, it quit in the air. Again "Low fuel Pressure". They tried a successful re- start. They made it down safely, and he loaded it and trailered it to my place for diagnosis. We talked to Lockwood, and Kitfox, and the best suggestion we could come up with was possible vapor lock. Unlikely in the air since it was cool that day. We began checking the fuel system end for end. Eventually we found the problem. The fuel line where it exited the wing and entered the fuselage had been fastened to the carry through inside the fuselage. This caused the lines to kink in the wing root when the wings were folded forward. When the tanks were full there was enough head pressure to keep the header tank full. When the head pressure went down, the kink prevented adequate fuel flow. What threw us a curve was there is a low level sensor in the header tank that never came on. Turns out it was defective. The "test" button on the instrument panel only tests the indicator light, not the unit.
We replaced the hoses with AEROQUIP steel braided hose, and put a new sensor in the header tank . Added two items to the preflight and run up to: 1. run the electric fuel pump without starting the engine and check the pressure to confirm it works, and 2. Run the engine with the wing tanks shut off to confirm the low level sensor in the header tank is working.