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Blue: The Holly carb used on Ford 3 cylinder gas tractors has a vacuum operated accelerator pump inside. Aside from being a wearing element in the die cast carburetor body, the pump makes the carburetor sensitive to vacuum related problems. Hesitation upon acceleration is a prime symptom of accelerator pump problems. These tractors also have both mechanical and vacuum spark advance mechanisms, both of which will affect engine vacuum. Thus static timing, mechanical advance problems (common) and vacuum advance servo failure (very common) will affect operation of the accelerator pump. Further complicating this situation: There is more than one version of these carburetors and overhauling a Holly carburetor with the wrong carb kit (again common) may render some carburetor circuits inoperative due to gasket mismatch. Finally, these carburetors are very sensitive to float level due to the accelerator pump, and the die cast carburetor body is prone to wear around the float pivot pin due to engine vibration. This makes proper float adjustment effectively impossible. All of these issues have contributed to the bad reputation earned by the Holly carburetors as used on the 3 cylinder Ford gas tractors. The Holly carburetor works well on the 3 cylinder tractors if everything is right but after all of these years that is ususually not the case. Good luck. Dean
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