This is a repeat of previous posts.
The drill method can work, but in some model carbs it can yield a carb set where the slides can't close completely or worse, can't achieve a proper idle RPM, because the slides can't close enough. I've seen this occur and also read about it here in this forum. A slide that can only close to a 1/8 inch opening produces and unloaded idle RPM of about 4-6000.
The light method makes the high idle speed issue vanish.
It goes like this.
Back out the idle knob so it can't effect slide opening position. Shine a light at the far end of the carb bore and find a slide that has the light blocked. Assign that carb as your master carb and/or make at least one slide fully close and block light, and assign that as your master carb. Don't make any further adjustments to this carb either on the bench or while performing a vacuum balance. The Master carb is the carb all others will be adjusted to match. Some carbs have no adjustment on #2 making it the default master carb.
Now that you have your master carb slide closed and blocking light from the other end, you adjust each carb slide in turn so that it *just* blocks light. You can verify your adjustment by operating the slides and ensuring that each slide blocks light at the same time when the slides move toward closure.
When satisfied, screw in the big idle knob so the slides are open about 1/16 of inch. This is so it can breathe enough to have an idle, and when the engine is running adjust the idle knob for 1000 RPM when the engine is at operating temperature.
You should still vacuum sync the carbs after a valve adjustment, to get a finer balance on the carbs and have all cylinders pulling the same amount. But, remember not to mess with the master carb adjustment. This will ensure you maintain full slide travel in all carbs.
Cheers,