Since the Holley 4165 is a spread-bore "Double Pumper," it features mechanical secondaries and external float adjustments. This makes it much easier to tune than models that require removing the fuel bowls.
Here is the step-by-step process to get your fuel levels dialed in safely.
1. Preparation & Safety
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Warm the engine: The engine should be at operating temperature so the choke is fully open and the high-idle cam is disengaged.
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Level the vehicle: Ensure the car is on a flat surface so the fuel level in the bowls is accurate.
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Have a rag ready: You will be opening "sight plugs," and a small amount of fuel may spill.
2. Check the Current Fuel Level
The 4165 has two fuel bowls (Primary and Secondary). You must adjust them individually.
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Locate the sight plug on the side of the fuel bowl.
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With the engine idling, carefully remove the plug.
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The Goal: The fuel should be right at the bottom edge of the sight plug hole. It should just barely "trickle" out if you gently rock the car.
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Too Low: No fuel visible.
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Too High: Fuel pours out of the hole (Fire hazard—shut off the engine immediately).
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3. Make the Adjustment
On top of the fuel bowl, you will see a large slotted screw sitting on top of a hex nut.
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Loosen the lock screw: Use a large flat-head screwdriver to loosen the screw just enough to allow the hex nut to turn.
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Turn the Adjusting Nut (5/8" wrench):
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To Lower the float: Turn the nut clockwise (down).
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To Raise the float: Turn the nut counter-clockwise (up).
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Rule of thumb: 1/6 of a turn equals approximately 1/16" of fuel level change.
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Clear the bowl: If you lowered the float, you must rev the engine slightly to "consume" the excess fuel in the bowl before checking the level again.
4. Lock it Down
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Once the fuel is at the bottom of the sight hole, hold the hex nut steady with your wrench.
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Tighten the lock screw firmly.
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Reinstall the sight plug.
