FAR 90-98B requires fuel flow test with the airplane in three different attitudes. Nose up 15 degrees, Nose down 15 degrees and Level. It took several days to complete all the test. Using the FAA formula for my engine it said I needed 20 gallons per hour or more for each test. My average flow per test was 54 gallons per hour. Fuel system in good shape. Put a cooling shroud on the mechanical fuel pump at the engine to help prevent vapor lock. High pressure pump is inside cockpit in the center tunnel, it will put up 32 psi dead headed. The level test and nose up were easy to do. The nose down test was done by removing grading in the taxi way and lowering the nose into the trench. Easy 15 degrees down. All test done with plane and all tanks grounded and fire extinguisher handy. I moved a lot of gas around. Before test were started both tanks had 5-10 gallons of gas put in and agitated then drained through a filtered funnel to catch any trash. This was done until NO trash showed up in the filter. Never any large amounts in any of the drainings.