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RF: Vintage Ford tractor carburetors are incredably simple but even an experienced carburetor person can overlook a problem issue or two if he is not experienced with them. The carburetor has a dual element float on a Y-shaped bracket. It fits into a tapered float bowl with one element on either side of the venturi. Because the bowl tapers toward the bottom, the float is sensitive to the float drop adjustment, which most rebuilders ignore. If the float drop is not set properly, the float may drop too far and wedge in the float bowl when you shut the engine off. The symptom is usually not apparent when the engine is running because the engine vibration prevents the float from sticking against the float bowl. When you shut the engine off the float may not lift shutting the fuel flow off causing the fuel to overflow the bowl into the intake air hose and eventually into the open intake valves causing a hydrostatic lock if the air intake hose is leak proof and (as is likely) the brass overflow in the air horn is plugged. Alternatively, the float could be leaking causing it to partially fill with fuel resulting in similar symptoms but I do not think this is your problem because nearly any carburetor repair person would have detected this. Since you paid a professional to rebuild it, I would remove it and have the rebuilder verify the float drop adjustment.
Dean
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