"......open idle mixture screws to 1 3/4 turns and adjust from there......"

Just to expand a little bit on what Jerry said.

The initial adjustment on the idle mixture is just that an initial setting.There is no set "turn them out so many turns and it is right". Carburetor, engine specifications, manifold design (both intake and exhaust), fuel, air pressure and humidity all have an effect on the engine idle.


You want the initial idle mixture rich enough to keep the engine running until it reaches operating temperature. General rule of thumb is to screw the adjusters in until they [I]lightly[I] seat and them back them out 1 1/2 to 2 turns (the amount you initially back them out usually depends on experience and preference).

Once the engine has reached operating temperature then you start adjusting the the mixture screws until you achieve the best idle. Some people us AFR meters or a vacuum gauge but most end up going by feel.

Start on one side or the other and adjust the mixture until you get the best idle then move to the other mixture screw. As I normally use 2 turns out as my initial setting it's generally a bit rich so I start by turning the mixture screw in until the engine starts to stumble just a bit and then back the screw out until it runs the smoothest, then move over to the other mixture screw and do the same thing. You might also have to reset the idle speed screw a bit as your adjust the mixture.

With dual carburetors I do one carb first then move to the other and them back to the first one etc etc until I'm happy with it.

Don't be concerned if the idle screws aren't set exactly the same once you're done. Manifold design and the different distances the fuel mixture has to go to get to the cylinders often requires just a little bit different settings.


.