In the words of Mr. Jon Haddock:
First of all, find a nice sized driver. I use a battery screwdriver head...fits nicely under the carbs and has flats for accurate counting!
Then, start her up and wait until she's idling about 200 rpm under normal...say 700. This is to allow for additional warm-up while idling. If you start from optimum idle speed it will get hotter still, and you will end up setting the carbs for an artificially hot condition never achieved during normal running...and it will be lean.
Re-familiarise yourself with the black idle knob and use it periodically to turn the over-all idle down to keep it below 1000...otherwise the needles come into play and you start to adjust for them...and it buggers things up!
Start on one side and, monitoring the idle speed by ear, turn the screw gently out until you 'peak' the idle speed. Go back and forth a couple of times to find the 'edges', where the revs start to tail off a bit, and go for the central point.
Repeat for the other side. Watch that idle...it WILL rise above 1000 so keep cranking it down.
Don't spend too long otherwise it will get hot and your optimum point will get progressively leaner.
Take your screw-driver with you next time you ride and if you have any popping, or want a couple more 'security blanket' goes, have a ...ahem...tweak on the roadside...makes you feel like a BritBiker!
- Jon Haddock