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There are no fewer than seven configurations of fuel systems for Ercoupes and two for Alons that have been unveiled over the manufacturing lifespan of the "Coupe." They all consist of variations of the same theme: An engine mounted continuous fuel pump draws from a line that connects both wing fuel tanks, and pumps fuel through a restrictor plug on the pumps output to the header tank. This restrictor reduces the pumps constant output to about 7 gallons per hour, which should keep up with the gravity flow of the header tank through a main shutoff valve to the gascolator and into the carburetor. Other proponents of the fuel system consists of finger fuel strainers in the bottoms of all tanks, elbows, equalizer lines, fuel caps, gascolator support brackets, and internal screens, along with the annually observed screen within the pump itself. When I discovered a problem with fuel starvation, it occurred in level flight, shortly after quite a bit of work had been done on the airplane. a cursory examination by the mechanic shortly after the incident showed there was fuel in all parts of the system! I took the airplane up again, and starvation occurred at exactly the same point in time that it had occurred before. This bore evidence to the fact that there was blockage of flow, or some sort of obstruction limited the amount of fuel available to the engine. Bad flexible fuel line! Has to be! No such luck!! The flex lines were all replaced, and the situation remained the same. Vapor Lock!! My mechanic, who doesn't talk much, went through a dissertation of liquids and pressures and boiling points complete with the amount of fuel passing a given point @ 6 GPH was in itself flow enough to prevent vapor lock regardless of temperature. I had no choice, in the face of such profound evidence, but to agree! He did submit a theory that finally was the culprit, that being a traveling bubble of air in the fuel system between the bottom of the header tank and the input to the carburetor. This air bubble could get into the system in a number of different ways, Carburetor servicing, Gascolator servicing, fuel line servicing, and running the header tank dry. Bleeding the air out of the line requires that the aircraft be level or slightly nose low, and the fuel line disconnected at the entrance to the gascolator, and flexed downward until the flexible portion of the fuel line is fully extended downward, allowing a considerable amount of fuel to flow unobstructed. ( about a pint) the line is immediately raised and connected to the input to the gascolator. This is a messy, scary process, that must be done outdoors in a well ventilated area. It takes guts. To explain this phenomenon:: a downward droop in a non compressible liquid line, can support an air blockage, and still pass some liquid, especially a liquid of low viscosity, Gasoline. The way this can happen is there is a layer of at least one molecule thickness between the liquid and gas called a meniscus which will allow the molecule of the heavier substance to travel along the solid wall, with the solid on one side of the molecule and the gas on the other. To make this more confusing; The gas is air, the liquid is gasoline, the solid is the material of which the fuel line is constructed. I hope i'm correct in my explanation, and it doesn't lead to a great deal of confusion. (Old Chinese Philosopher) To prove this point, we drained the header tank through the gascolator quick drain, and filled up the header tank. I could get the engine to idle and taxi around, but when I applied full power, the engine ran at full power for about 45 seconds and quit. We bled the system as described previously, and topped off the tank, resumed the run up, taxi and takeoff test, and the airplane operated flawlessly. This is assuming that certain criterion have been met in the aircraft's fuel system; The 1 piece venturi has been installed, along with the new needle valve and seat and the plastic float. The Aluminum fitting between the gascolator and carburetor has been replaced with a brass, or steel fitting. The brackets supporting the gascolator have been installed. The fuel strainers have all been inspected within the inspection time frame, and properly reinstalled. The vents are clear in the fuel caps and pointed forward. The fuel caps are properly gasketed and seated flush with the seat of the tank filler neck. The straps supporting the header tank are not broken free allowing the tank to rest on the bicycle chains of the control column. This puts a crimp in the fuel line exiting the bottom of the header tank restricting flow on the way to the engine compartment. Examining the entire fuel delivery system in your "Coupe" may reveal one or two little anomalies that have a tendency to compromise the efficiency of the overall system, a system which relies only on the weight of the fuel in the fuel line to keep the fan flowing. One other little memo. If the tail is low it also compromises the fuel system continuity while fueling. Makes no difference in the air, but it could still be a candidate to the introduction of an air block. This is a description of what I found on my airplane, and is no way intended to be critical of others and their treatment of their aircraft. Thanks for listening Wayne -- Mr. D. Wayne Woollard, CPBE AIM: DWWoollard ICQ: 124132836 "Why fly a Spam can when you can have fun and fly an Ercoupe?" ================================================================== TO UNSUBSCRIBE go to: http://ercoupers.com/lists.htm
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