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Thread: How do I adjust WOT mixture on Vacume Carb?

  1. #1
    I just bought a Holley 750 cfm Vac Sec carb for my boat that has a chevy 350 in it. It runs a little lean a wide open throttle (plugs are bone white with just a hint of light tan). Since there is no secondary metering block on the 750 vac. Secondary carbs (just a pre drilled metering plate), is there any way for me to richen up the mixture at WOT without changing the primary jets? I've heard that raising the float level on the secondary bowl will richen it up a bit at WOT, is that true? Can I just buy a stock metering block from Holley and put in on this carb so that I'll be able to chancge jets on the Secondary side? Thanks for the help.

  2. #2
    You can buy a Holley conversion 4150 metering block for that Vacuum secondary so there is adjustability with the Jets. That might sure you, but the springs in the vacuum pump need to be tailored to your specifications also.
    I can perform the secondary metering block conversion that also includes a redone "idle circuit" where you can have completer 4 CORNER IDLING adjustability. Just email me and let me know.
    Another option is to switch to a 650 Double pumper and ditch the 750 3310

  3. #3
    Hello.........Hey easier way is to convert to a Billet jet plate with threaded holes for standard jets that replaces the standard jet plate in your holley......this way also your fuel line length stays the same without having to buy another fuel line.....I have these plates if interested,they sell for $29.00 and include the jets needed to get a starting point.....The 3310 carb will work just fine........just rchen the secondarys a little to color your plugs.....Good Luck, Jesse @ BIGS

  4. #4
    Why don't you just pop off the rear fuel bowl and replace the secondary metering plate with the next-up size ? I think there are 4 or 6 odd-shaped set screws to remove the plate. Holley makes a selection of these with varying sizes and I'd imagine they are available at most speed shops. I've got about a half-dozen different sizes myself.
    I don't believe that raising the rear float levels is the correct thing to do. For further info, contact Dave at Fuel Curve in Upland CA. I can't say enough good things about him - very helpful and informative.

  5. #5
    Hi Bigs, welcome to the board. Its nice to have someone in the carb biz helping out on here.

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