Since the Carter WO (standard on the Willys MB and CJ-2A) is a "counter-shaft" style carburetor, the metering rod must be perfectly synced with the throttle position. Usually, you’d use a T109-102 gauge, but you can get it spot-on using a standard drill bit or a caliper.
The goal is to ensure the rod is fully "seated" (at its leanest point) exactly when the throttle plate is closed to a specific gap.
Tools You’ll Need
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A 0.054" Drill Bit (A #54 wire gauge bit is ideal, or any shim of that thickness).
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Small Flathead Screwdriver.
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Pliers (for gentle bending of the linkage if necessary).
The Adjustment Process
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Back off the Idle Screw: Turn the throttle lever adjustment screw (the idle speed screw) out until the throttle plate is fully closed and seated in the bore.
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Insert the Shim: Insert your 0.054" drill bit between the throttle plate and the carburetor bore (on the side opposite the idle port). Hold the throttle lever against this bit so the butterfly is "propped" open exactly 0.054".
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Check the Rod Position: Look at the metering rod arm. The metering rod should be bottomed out in its well at this exact moment.
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The "Finger Test": Push down lightly on the flat part of the metering rod arm. There should be no downward play, but it shouldn't be under heavy tension either.
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Adjust the Nut: If the rod is too high or too low, loosen the small nut on the pump arm that holds the metering rod link.
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Move the link up or down until the rod hits the bottom of the seat just as the throttle hits that 0.054" gap.
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Tighten and Verify: Tighten the nut and remove the drill bit. Open and close the throttle a few times to ensure the rod moves freely without binding.
Why the 0.054" Gap?
In the absence of the Carter gauge, this measurement ensures the "step" on the metering rod moves out of the jet at the correct vacuum transition point. If it’s set too high, you’ll run rich at idle; too low, and you’ll have a nasty flat spot when you step on the gas.
Pro Tip for Your Bench:
Since you're working on this in the shop, make sure the anti-percolator valve (that little cap on the top) is also clearing its seat by about 0.030" when the throttle is cracked. If that isn't opening, you'll have a hard time restarting the engine when it's hot.
