I was looking more for an empirical number. I'm currently set at 800rpm. Not really close to the "book" value specified...
Which book value are you referring to? There are some numbers on microfiche #30 which maybe Johnny Tillotson has, but I doubt any of the equipment listed on it will be "mini bike."
I never use a tach on these vintage engines. I adjust the idle until it is low enough to not engage the clutch. I don't want any clutch expansion what-so-ever, as it wears out clutches and burns up the lubrication on the bushing.
But I don't turn the RPM down so low that the slinger isn't lubricating the bottom end either. Also, in hot weather, or on slow or stationary equipment, you need enough RPM to cool the engine with the fan.
Sorry if this is not the level of detail you are looking for, but it's how I do it. I'll assume you know the idle adjustment procedures on non-emission engines with adjustable jets, but because I was there, I cut and pasted the book procedures below.
And a correction for a comment made above. The main jet does not come in to play on "this" carburetor at idle. If it is drawing off of the idle transfer passage at idle. If it is drawing off the main jet, it is idling too high. However, the idle setting is additive when transitioning to high RPM and at WOT. Not the other way around. Pretty common method of idle feed on bowl type carburetors.
FINAL ADJUSTMENTS (NON EMISSION ENGINES)
Start the engine and allow it to warm up to normal operating temperature (3 - 5 minutes). Set the speed control to the HIGH or FAST position. From the recommended preset position, turn the main mixture adjustment screw in (clockwise) slowly until the engine begins to run erratic (lean). Note the position of the screw. Now, turn the screw out (counterclockwise) until the engine begins to run erratic (rich). Turn the screw in (clockwise) midway between these two positions. This will be the best setting. (diag. 21, 22 & 23). Set the speed control to the IDLE or SLOW position. Adjust the idle mixture screw following the same procedure used to adjust the main mixture adjustment screw.
If further adjustment is required, the main adjustment should be made under a loaded condition. If the engine stops or hesitates while engaging the load (lean), turn the main mixture adjusting screw out (counterclockwise) 1/8 turn at a time, testing each setting with the equipment under load, until this condition is corrected.
If the engine smokes excessively (rich), turn the main adjusting screw in (clockwise) 1/8 turn at a time, testing each setting with the equipment under load, until this condition is corrected. After the main mixture screw is set, move the speed control to the IDLE or SLOW position. If the engine does not idle smoothly, turn the idle mixture screw 1/8 turn either in (clockwise) or out (counterclockwise) until engine idles smoothly.
Recheck the high and low R.P.M. setting and adjust as necessary.