Howdy,

Now that you know the direction to turn the jet to set IDLE leaner, you can make IDLE as lean as you want. But, the leaner IDLE setting will have minimal effect on the CRUISE mixture. If you have a clean transition from idle to part throttle I would not touch the IDLE mixture adjustment.

I assume the goal is to lean the carbs at cruise? To change the CRUISE mixture you must swap needles. If you do not have an educated choice of needles to swap, and the understanding of how to tune the carbs at idle, part throttle, and wide open throttle you are much better off running a bit rich at CRUISE.

If you really want to set CRUISE mixture leaner you must study the SU carburetor until you can truly say, "I know exactly how these things function." Then determine the needle set that are one step, two steps, and three steps leaner (I don't think you will need to go leaner than that) at CRUISE while leaving the IDLE and OFF-IDLE dimensions as they are. (Unless you also need to adjust idle and transition.)

The actual tuning is much easier with a wide band O2 meter but can be done with no tattle-tale if you know how to read the plugs.

--
Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 53 year old fat man. ;-)

You're getting the answer correct but coming to it the wrong way. You describe looking straight down and asked--which way does it go? But that makes as much sense as looking at it straight up--in which case the lean/rich directions reverse. We look at the carbs from the side so if you understand what the screw adjustment is doing you won't get confused. Vertical screw thread - turn the nut so it moves up the threads for lean - down the threads for rich. I relate to things visibly so I understand your desire to visualize it from a known vantage point--my only point is to make that vantage point the one we actually use which will lead to a better understanding of the mechanics involved. -- Dave