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Positive Pressure Tank Prime
I believe it was Herb from the Kolb List, who mentioned that he did not use a squeeze bulb but forced the fuel up to prime the fuel pump and carburetor with positive pressure. I thought this was a good idea for system simplification and weight reduction. Since I carry a tiny bicycle tire air pump in the FireFly, I had a good pressure source. I purchased a short tubeless tire stem and drilled the tank and popped it into place. The tire stem valve was removed. To boost fuel to the engine one puts the tire pump and valve extension, as described below, on the stem and increases the pressure sufficient to prime the float bowl. When the pump and extension is removed, the stem acts as the tank vent.
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The problem with the bicycle pump alone, is that it depends on the stem valve to keep the air from returning to the pump on the return or fill stroke. The minimal weight way to get around this is to make a valve stem extender that includes a valve. This was done by purchasing a short valve stem and removing all of the rubber vulcanized to the brass stem. Then the gasket was removed from a brass cap and a hole drilled to accommodate the stem OD and it was soldered into place. Then the gasket was returned to its original position.
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Here is the completed extension. This change gets rid of the squeeze bulb and reduces FireFly dry weight by two ounces.
Then as I came up on the Tillotson carburetor learning curve, I discovered, one cannot force the fuel up to the carburetor, and so, no fuel line squeeze bulb or positive tank pressure is required. All one needs is a fuel line, line shut off, and in-line filter. The carburetor push button primer will lift fuel from the tank.
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