Good call as usual, TwoMany!
Peanut, there's a pilot circuit and a main circuit, there is no "idle circuit;" control of idle mixture is one pilot circuit function. You can post all the winks and smilies you want to, the fact remains that if you fool with needle position you'll get secondary effects even at idle. Also, you will not have slide lift on old round slide BS series carbs with throttle set to turn 1500 rpm. What you will have is the throttle plate opening the pilot circuit bypass/transition nozzles (smaller holes) in the spigot and a resulting increase in vacuum through the slide cutaway.
As 5twins has pointed out many times, the heavy slides on older BS-series carburetors don't start to lift before around 4K rpm, so that in much of the cruising range the pilot circuit is the primary metering system. But with increased vacuum, the main circuit is in play even with the slide down. In later BS-series carburetors with light semi-flat slides, lift occurs much sooner; they're different beasts entirely.
One more time: most component-and-range charts are written with reference to carbs with mechanically lifted slides, and are virtually useless in working with vacuum carburetors, particularly older designs.
Peanut, there's a pilot circuit and a main circuit, there is no "idle circuit;" control of idle mixture is one pilot circuit function. You can post all the winks and smilies you want to, the fact remains that if you fool with needle position you'll get secondary effects even at idle. Also, you will not have slide lift on old round slide BS series carbs with throttle set to turn 1500 rpm. What you will have is the throttle plate opening the pilot circuit bypass/transition nozzles (smaller holes) in the spigot and a resulting increase in vacuum through the slide cutaway.
As 5twins has pointed out many times, the heavy slides on older BS-series carburetors don't start to lift before around 4K rpm, so that in much of the cruising range the pilot circuit is the primary metering system. But with increased vacuum, the main circuit is in play even with the slide down. In later BS-series carburetors with light semi-flat slides, lift occurs much sooner; they're different beasts entirely.
One more time: most component-and-range charts are written with reference to carbs with mechanically lifted slides, and are virtually useless in working with vacuum carburetors, particularly older designs.
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