How To Straighten IH Updraft Carburetor Tops

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Dan England
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How To Straighten IH Updraft Carburetor Tops

Postby Dan England » Wed Sep 26, 2007 5:35 pm

The IH 3/4" Updraft Carburetor used on Farmall/International Cub and Lo-Boy tractors is excellent in function and durability. Some are sixty years old, are still in use and are functioning very well. Probably the most commonly occuring problem is warping of the top, brought on by overtightening the four screws that attach the top to the body of the carb. This article presents a method of restoring the top to its original shape.
    How To Straighten IH Updraft Carburetor Tops

    Tools Required:
    • Platform
    • four “C” clamps
    • four small flat washers

    • Preparing the Platform:

      The size of the platform can vary but the one used here measures 6" X 6" and is 1 1/4" in thickness. The top is milled smooth to create a flat surface needed to straighten the carb top. Two holes are milled into the platform. The circular one is 1 1/16" in diameter and is 1/2" in depth. The oval opening measures 7/16" by 1 1/16" and is 13/16" deep. The bottom of the throttle body assembly fits into the circular opening while the two arms of the float assembly occupy the oval one.


      Preparing the Carb Top:

      Remove the top from the body of the carb and lay the body aside. From the top remove and lay aside the fuel bowl gasket, float and float lever, the cage assembly, gasket and float needle valve, and idle adjusting needle valve and spring. VERY CAREFULLY, remove the idle tube.



    • Procedure for Straightening Top:

      Place the carb top on the platform, fitting the throttle body extension into the circular opening and the float assembly arms into the oval one. The outer margin of the ventral surface of the top should contact the upper surface of the platform except in regions where the top is warped. Generally, the two surfaces will mate in the regions of the screw holes of the top. Gaps between the surfaces, if present, will be in the areas between the screw holes. Use “C” clamps to close the gaps between the top and platform. In badly warped areas, closure should involve several steps of tightening the clamps with a rest period between to allow metal to adjust. Small gaps can be closed in a single operation. Additional straightening, if needed, can be achieved by placing flat washers between the screw holes of the top and the underlying platform.


Platform prepared by Jesse Roberts of Monroe, LA
Last edited by Barnyard on Wed Jan 31, 2018 12:29 pm, edited 1 time in total.
Reason: Added Missing Images

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