66 327/300 Heat Riser vs Holes Under Carb - NCRS Discussion Boards

66 327/300 Heat Riser vs Holes Under Carb

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  • Anthony D.
    Infrequent User
    • February 24, 2014
    • 11

    66 327/300 Heat Riser vs Holes Under Carb

    In Oct 2014 I cut out the flap in the heat riser and tapped and plugged the 2 holes under the carb.
    Car ran great here in So. Cal.
    Now I am preparing the car for a PV and have installed the proper heat riser.
    My question is, do I need to remove the plugs under the carb?
  • Joe L.
    Beyond Control Poster
    • February 1, 1988
    • 43221

    #2
    Re: 66 327/300 Heat Riser vs Holes Under Carb

    Originally posted by Anthony Damico (59660)
    In Oct 2014 I cut out the flap in the heat riser and tapped and plugged the 2 holes under the carb.
    Car ran great here in So. Cal.
    Now I am preparing the car for a PV and have installed the proper heat riser.
    My question is, do I need to remove the plugs under the carb?

    Anthony------


    No, you definitely don't need to remove them and I highly recommend that you do not remove them.
    In Appreciation of John Hinckley

    Comment

    • Timothy B.
      Extremely Frequent Poster
      • April 30, 1983
      • 5186

      #3
      Re: 66 327/300 Heat Riser vs Holes Under Carb

      Anthony,

      I agree with Joe, FWIW the hot slot in the manifold under the carburetor is there to heat the carburetor base during engine warm which prevents ice from forming around the throttle blades.

      Comment

      • Robert B.
        Very Frequent User
        • May 31, 2005
        • 163

        #4
        Re: 66 327/300 Heat Riser vs Holes Under Carb

        Tony, you mentioned that the car did not idle well after you installed the heat riser, and it had been running fine before you installed it. That tells me you may have some back pressure building up on the passenger side. I'm pretty sure I remember reading on this forum that you are advised to either remove or keep open that heat riser when you block the hot slot in the manifold.
        Easy way to check is wire the heat riser open, start the engine and see if it's running the same - if it is, then it's time to check the carburetor, if it runs fine, it has to be caused by the blocked hot slot.

        Bob

        Comment

        • Joe L.
          Beyond Control Poster
          • February 1, 1988
          • 43221

          #5
          Re: 66 327/300 Heat Riser vs Holes Under Carb

          Originally posted by Robert Behlman (44041)
          Tony, you mentioned that the car did not idle well after you installed the heat riser, and it had been running fine before you installed it. That tells me you may have some back pressure building up on the passenger side. I'm pretty sure I remember reading on this forum that you are advised to either remove or keep open that heat riser when you block the hot slot in the manifold.
          Easy way to check is wire the heat riser open, start the engine and see if it's running the same - if it is, then it's time to check the carburetor, if it runs fine, it has to be caused by the blocked hot slot.

          Bob

          Bob------


          The heat slot in the front of the carburetor flange, while supplied with heat through the cross-over in the manifold, is not otherwise related to the heat riser valve. If the heat slot is eliminated by the plugging of the holes on both ends, neither the engine or the heat riser valve "knows the difference". In fact, many engines never even had the heat slot and NO engines after 1969 had it. They had exhaust cross-over and heat riser valves but no heat slot. The heat slot is the biggest "carburetor destroyer" ever invented.
          In Appreciation of John Hinckley

          Comment

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