Checking fuel mixture on #MGB

Below is an extract from the SU Carburettor Manual downloadable at

The procedure also applies to HIF carbs as well.

The only comment i would make relating to these instructions is not to use the button on the side of the carb as it’s just about impossible to know you’re lifting the 1/16″!!. Better to take air filters off and lift the piston with your finger or screwdriver so you can see piston rise …….. it’s easier to judge the 1/16″.

The next best way i find to check fuel mixture is by looking at the colour of the spark plugs after a decent run in the car …….. see

Note: To richen mixture on HS4 carbs screw the mixture screw out, on HIF4 carbs screw in (clockwise)

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