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My 340 is running so rich I can't even go near it when it's running. Other than the simple 2 screws how do you adjust the mixture to lean out a thermoquad? It's a 6138S if that makes any difference.



Be sure the carb base gasket is an open center spread bore gasket, not a 4 hole gasket.

Also you can bump up the initial timing two degrees and back off the main idle speed to lean the idle circuit.

You can dial-in the idle circuit by using a vacuum gauge on the driver rear port on the base. You need to adjust each idle mix screw for the highest vacuum reading.

There is also a center adjuster slot at the top of the metering rod tree. You can adjust this screw for the highest vacuum reading also, David.

***pic shows best idle speed adjustment before carb installation or at any point that the main idle speed adjustment is unknown on a stock application*** You want only a square showing at the front edge of the primary butterflies on the idle transfer slot. Hole at the top is where the tip of the idle mix screw ends.

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