"Low-speed jet"- - - - -are you thinking about the idle mixture jet, the one that screws into the carburetor body just above the throttle plates? If so, start by gently closing the needle valve all the way clockwise and turn it back counterclockwise about 1 1/2 to 2 turns. This should allow the engine to idle until it warms up sufficiently for a final adjustment. Attach a vacuum gauge to a full manifold vacuum source like the windshield wiper hose port. With the engine idling at around 400-600 RPM, turn the idle jet clockwise until the vacuum starts to drop, and then back it out until the vaccum maxes out. It might be necessary to slow the idle speed down to get the best compromise between idle speed and steady vacuum. A good idle vacuum reading will be 17 to 19 inches of mercury, depending on your camshaft, ignition timing adjustment, and general health of the engine.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!