carb question

[larry harding]

i have a couple of engines with the cast carb and one with the white (pot)) metal carb. i know that the choke rod also adjusts a mixture screw, but don't know what this is for . low speed, main jet or what or how it should be set. i have the "les" books and it is only called an adjusting screw. can someone fill me in on when and how this is used. i know that somewhere in the books there is a reference for this question, but i haven't found it yet.

[Patrick L.]

The 'choke rod mixture screw' is the GAV. All the way is lean and richer as its backed out. Zeniths run well from all the way the in to about a 1/2 turn out. The Tillotson will run best from 1/2 to 1 turn out.
In cooler weather many folks back the GAV out another 1/2 to 1 turn to start and for a few miles.

There is another adjustment screw for low speed/idle mixture located near the idle speed adjustment screw.

[BILL WILLIAMSON]

The GAV turns off & on/adjusts an extra jet that supplements the MAIN jet, when it's running too lean.
Chief taught me how to adjust it: With a WARM engine, run at a constant speed of 20 to 25 MPH, in second gear & adjust it for BEST, SMOOTHEST running, "Then, don't diddle with it"!! Well, that's whut he sed.
Bill W.

[Tom Wesenberg]

I turn my GAV out about 2 turns when I start the engine cold. As it warms up during the first minutes or two I can turn it back in between 1/4 to fully closed.

[larry harding]

thank! sounds like this works with the main high speed jet.

[Mike V. Florida]

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Originally Posted by larry harding

thank! sounds like this works with the main high speed jet.

This may help,

model a carb basics