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Customs Let's discuss updraft carb theory

Discussion in 'The Hokey Ass Message Board' started by Deere boy, Jul 10, 2019.

  1. Deere boy
    Joined: Jul 25, 2018
    Posts: 45

    Deere boy

    The engine on the John Deere speedster I posted photos of here a couple of days ago is a two cylinder flathead with an updraft TSX carb. The engine originally came from a small pull type combine or small tractor, and thus has a governor which I have hooked up. I was showing it to my mechanically inclined BIL and brought up the possibility of disengaging the governor and hooking the accelerator pedal directly to the carb throttle valve in a more car-like fashion. He told me if I do that, with the updraft carb with no accelerator pump, I will be killing the engine frequently because it won't be reactive enough. Is this true?
    Photo below show the engine in its natural state.
    tractorguy likes this.
  2. samurai mike
    Joined: Feb 24, 2009
    Posts: 417

    samurai mike

    if it works don't fix it.
  3. Deere boy
    Joined: Jul 25, 2018
    Posts: 45

    Deere boy

    It works, but it's not very car-like.
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 42,667


    I don't recall seeing an accelerator pump in a Model A ford carb, and they seem to do ok.
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  5. Fabber McGee
    Joined: Nov 22, 2013
    Posts: 720

    Fabber McGee

    I would say no, no change in performance and no stumble. Your engine is basically a heavy duty version of a Briggs and Stratton low performance industrial engine. It has very low fuel demands and low power production. Also I would expect a very heavy flywheel. It won't accelerate quickly enough to need an accelerator pump. All the governor does is limit RPM, it will still slam the throttle wide open when you ask it to.
    The only advantage I can see to bypassing the governor is removing the top speed limit by not letting the governor control maximum engine RPM.
    carbking and tractorguy like this.
  6. carbking
    Joined: Dec 20, 2008
    Posts: 2,477


    The first mechanical accelerator pump came out circa 1932. There were some "syringe pumps" in operation by about 1921; however, the output of the syringe pump was maybe 5 percent of that of the mechanical accelerator pump.

    Virtually all updraft carburetors THAT HAVE ACCELERATOR PUMPS use a vacuum pump rather than a mechanical pump. The pump reacts to the lowered engine vacuum after the throttle has been opened. Never really considered what percentage of updraft carburetors have accelerator pumps before; but it isn't very high.

    Lots of updraft carburetors with no accelerator pump were used on non-governed engines.

    And that picture needs to be in living color. Everyone knows that all real tractors are painted green and yellow!:cool::):D


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