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Thread: Tillotson Replacement Base

  1. #1
    Join Date
    Mar 2005
    Location
    Huntington, New York - American Zone
    Posts
    801

    Default Tillotson Replacement Base

    I'm assembling a later ('D'-Series) Tillotson carburetor for my 1970 XLCH and noted that Ted sells replacement white plastic bases. While I have several original used bases, they have yellowed as most do and the new white base would look so good on my '70 when its completely restored.

    I received the base and it really looks great. In fact, I suspect that its probably sourced directly from Tillotson. The fit onto the carburetor body is perfect and the accelerator bore-to-pump also fits very well.

    However, the new base didn't come with the small accelerator check ball and its brass retainer. Furthermore, the hole for the ball and retainer is too small for the check ball and its not stepped to accommodate the retainer, as is the O.E.M. Its interesting that the exploded diagram in the Sportster Service Manuals shows these two parts, but the Sportster Parts Catalog does not. This probably means that when you purchased a new base from Harley, it came with the check ball and retainer already installed. This is probably how Harley-Davidson received them from Tillotson. This makes sense, as the ball/retainer are difficult to work with, especially using these 70 year-old fingers!

    Further complicating the issue is that on the O.E.M. bases, the upper portion of the stepped hole is sized larger than the ball's bore size so that the retainer can be pressed-in. The larger step diameter is not a standard drill size and to properly re-drill the existing hole in the new base you would have to have a custom cutter made.

    So I drilled the new hole out to fit the ball, but had to slightly over-size the upper step so the retainer now isn't a press-fit. I'll nave to figure out how to make it stay - probably with a small dab high-strength epoxy.

    After all of the hot air above, my question is whether or not anyone else has purchased one of these bases and if so, what your experience with it has been. How did you fit the retainer? How well does the part work on an operating carburetor?

    I've written to V-Twin and await an answer. In the past, they've always responded to my inquiries and have helped whenever possible. However, if I can't get it worked out through V-Twin, I guess my next step is to contact Tillotson directly. Hopefully, they'll speak directly to me.

    Any suggestions??
    Last edited by Bill Pedalino; 09-29-2019 at 03:49 PM.
    Bill Pedalino
    Huntington, New York
    AMCA 6755

  2. #2
    Join Date
    Mar 2005
    Location
    Huntington, New York - American Zone
    Posts
    801

    Default

    As a follow-up to the above posting, I received as response from V-Twin stating that the carburetor base re-manufacturer (apparently not Tillotson) is not willing to install the check ball assemblies into their carburetor bases. I've also been informed by another AMCA member that the earliest Sportster Tillotson bases (1966) did not have the check ball assemblies.

    In figuring out what the check ball's intended function is, and having studied the fuel flow diagrams in my 1959-1969 Sportster Service Manual (pages 3F-2 and 3F-3) it looks like the check ball is to aid in holding a fresh charge of gas in the accelerator pump channel located between the top of the diaphragm and the carburetor's main bore. It also appears that the flapper portion of the diaphragm (alone) was originally intended to act as this back-flow prevention mechanism and the check ball was subsequently added to assist. This seems to make sense, as these service manual diagrams were probably drawn in 1965 and not updated after 1966.

    If anyone knows more about the above, please inform me, as installing these check balls into new bases is very laborious and I'm wondering if its and update that you can live without.

    Thanks....
    Bill Pedalino
    Huntington, New York
    AMCA 6755

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