Fuel Return Line
On a carbureted Cobra, the engine compartment heat, particularly when combined with high altitude and poor fuel can contribute to fuel boil over and poor performance. One way to help this problem is to keep the fuel cooler. To do this you can add a fuel return line. The return line keeps the fuel circulating so that the fuel in the line is closer to the temperature in the fuel tank. This article details adding a return fuel line to a Suprformance Mark III
Carburetor fuel log with return line. The fuel inlet AN-6 hose enters the rear of the fuel log and a AN-4 hose, the return, exits the front. The return hose and routes down the passenger side of the tunnel where it connects to 1/4" aluminum tubing.
Below you can see the AN-4 fitting, which is the beginning of the return line
To provide enough restriction to maintain 7 psi fuel pressure, a restrictor is used as shown below. The restrictor is a 10-32 Allen head set screw, with a .060" hole drilled through it and screwed into the AN-4 fitting used at the front of the fuel log.
The photo below shows the routing of the return fuel line into the Fuel tank. The fitting/union was custom made to fit over the existing fuel tank vent nipple. It now accommodates the returning fuel as well as the vent.
Below is a sketch of the return union
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