Holley carb guru's - adjustment inconsistencies - NCRS Discussion Boards

Holley carb guru's - adjustment inconsistencies

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  • Timothy B.
    Very Frequent User
    • January 1, 2004
    • 438

    Holley carb guru's - adjustment inconsistencies

    I have noticed inconsistencies in the specs for adjustment of key C2 Holley carb settings between the various sources of data. I am hoping that others have experienced this and might have some knowledge on which source is the "best" to use or other insight. My car is a 67 327 with 3810 type carb, but these inconsistencies apply to many models.

    For performing a carb rebuild or adjustment sequence, you can refer to these sources, all of which I have:

    1). Data sheet included with Holley rebuild kit.
    2). Factory Chevy Service Manual (CSM) from the year of the car.
    3). Holley official 4160/4150 technical service instruction guide (from Holley, my copy is from the early 70's).
    4). Holley service and reference manual from third party publisher.

    Here are some of the inconsistencies:

    A). Dry float settings. For carbs without externally adjustable floats, the data for float settings differ between the rebuilt kit and the CSM. Also, the data sheet says to measure the setting from the "tip" of the float to the float bowl. The CSM doesn't specify where to measure from. The Holley manual specifically says to measure from the tip on the primary bowl only and the heal of the float on the secondary side. All of these would produce significantly different float levels depending on which you follow.

    B). Secondary throttle stop adjustment. The data sheet with the rebuild kit and the Holley service manual both say to adjust the small screw the point where the secondary plates are completely closed, and then turn the screw in 1/4 turn after making contact. The CSM says turn in 1/2 turn after contact. On the car, this results in a significant difference in how the car idles.

    Those are the major differences I have found, but I think there are others particularly in how the choke is set. Comments?
  • Mark B.
    Expired
    • February 1, 2004
    • 138

    #2
    Re: Holley carb guru's - adjustment inconsistencie

    Tim,

    First, I sympathize with you. Holley tuning can be quite confusing. Second, the float measurements are only for getting you in the ballpark until the engine is idling and you can set the "wet" float level while the engine is running and the sight plug is removed with fuel just "seeping" out of the opening. I usually set the secondary float lean by not allowing any fuel to seep. This assures me somewhat that fuel will not be drawn into the carb from the secondaries during shutdown and hot soak periods.

    Unless you have a 4-corner idle circuit in your carb, just adjust the screw 1/4-turn to open. Then adjust your idle using the primary throttle blades and metering screws. On cars with very aggressive cams, you need to let more air in at idle and thus the secondaries can be adjusted to allow this to happen. Consequently, the primary metering screws would also need to be adjusted rich to compensate. Good luck.

    Comment

    • Timothy B.
      Very Frequent User
      • January 1, 2004
      • 438

      #3
      Re: Holley carb guru's -adjustment inconsistencies

      Thanks for the reply. Unfortunately, the 3810 carb doesn't have externally adjustable floats, and there is no sight plug. The internal adjustment is all you get.

      Comment

      • Mark B.
        Expired
        • February 1, 2004
        • 138

        #4
        Re: Holley carb guru's -adjustment inconsistencies

        Tim,

        Since it doesn't have external adjustment, I have found that the easiest way to adjust the floats on pretty much every carburetor I have worked on, is to have the top of the float parallel with the float bowl with it inverted. I have never figured out how to adjust any float to 1/32- or 1/64-inch with my bifocals and hand tools!!! For me it's unrealistic. However, my method, although somewhat crude, has always worked, and worked well. Good Luck.

        Comment

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