What do the fuel/air screws do and how does it affect the engine?
If you open them 2 turns instead of 1 1/2 turns what does that do?
If you open them 2 turns instead of 1 1/2 turns what does that do?
actually they are fuel screws on the yamaha flatslides, by opening them up to 2 turns from 1 turn your making the fuel circuit(idle) richer. If you have a engine that has a stumble on take off, or the idle seems to hang up before dropping down after you gas it, this would be when you would want to add more fuel to the circuit. You can generally adjust them out to about 2-2 1/4 turns out before you should go to the next size up in pilot jet. Some others may like to turn them out further, but your kinda shooting yourself in the foot, because once you get past 2 1/4 out, you need a bigger pilot jet.
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When does this circuit cutout and the needles take over ? I assume the needles are the next part of the carb that meters gas!?
fuel screws really only work up to the pilot circuit, the pilot, controls the low end, then the needles, then the mains. The circuits kinda overlap one another so you are only on the fuel screws for a instant, then right on the pilot jet, as soon as it gets a 1/3rd way into throttle, your on the needles, till about 3/4 to wide open your on the main jets. Pilot jets and the needle taper and nozzle do contribute to total fuel flow however.
Thanks for the info Mr. Viper!