How to Check the Fuel Level in the Carburetor

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Lurker Carl
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How to Check the Fuel Level in the Carburetor

Postby Lurker Carl » Sun Apr 01, 2018 12:16 pm

You can mount the carb on the tractor. I find this way is easier to take the carb apart to adjust the float height if it needs it. This is the ‘heavy’ float carb, and I’m sure I’ll take it apart a few more times.

I made a fuel level gauge out of a piece of 3/8 O.D. plastic tube and translucent silicon tubing. The tubing must be resistant to gasoline! I sealed the threads with a glob of plumber’s putty (on the outside) and marked the silicone tube every 1/16 inch for one inch. Then I clamped the carburetor under the work bench, swiped the fuel line from the Cub and attached it to an old B&S gas tank with a shut off valve hung from the ceiling. There is a catch pan under it to contain any spills. Open the valve, watch the fuel level rise in the tube and read the results.
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This is a ‘heavy’ float. It has 3 large globs of solder on it, adding unnecessary ballast that can cause the float to ride lower in the fuel and over fill the fuel bowl. I’m interested in seeing what the fuel height is with the carburetor installed on the tractor, with the float height set to specification. This Cub (Smoky) always ran rich, so much so it didn’t need the choke to start except in cold weather.
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Measure the head space in the fuel bowl from the top of the gasket down to the fuel level. As I earlier suspected, the ‘heavy’ float is less buoyant and allowed the fuel level in the bowl filled to 3/8 inch from the top. IH specs say 9/16 – 5/8 inch. It’s ¼ inch too full. So, I shut off and drained the fuel, disassembled the carburetor and increased the float height from 1.4 to 1.6 inches, rechecked the float drop, put it all back together and repeated the test. The fuel level dropped to 5/8 inch from the top. Inside this little carburetor, such small differences can make big problems.
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