Fuel flow checks
January 1989
As called out in CP 53 have caused a number of builders some confusion. We even rechecked our numbers to be sure we had not made a mistake! Mike and Sally's Long-EZ and Burt's Defiant are both relatively old (8 years and 11 years) and the electric fuel boost pumps were also this old at the time of the tests, as were the mechanical fuel pumps. Since we have installed new Facet electric boost pumps on both of the above aircraft, we also cannot get the fuel flows called out in CP 53. We believe that the foot valve springs in the new pumps must be creating enough restriction to fuel flowing by gravity, that it is impossible to obtain the flow rates called out in CP 53. Of course, the "fuel pump on" tests are still relevant and nothing has changed in this test.
We believe, now, that the gravity flow check must be conducted by removing the gascolator bowl or breaking the fuel line at the gascolator. You should be able to achieve the flows shown in CP 53 using this method for the gravity flow ' check. You should re-connect the fuel line at the gascolator for the "fuel pump on" test and break the fuel line at the carburetor. Again, you should be able to achieve the flows shown in CP 53. If you cannot get at least the correct flows shown, you may have a restriction in the fuel lines or fuel valve. This restriction must be cleared before flight.