72 750 roadster

You tune the idle at operating temperature for best running. You should retune for best idle when fully warm.

This means by default it is not tuned well for idle when cold and so needs some revs to keep it running until some warmth is in the engine, it's not a modern ECU controlled fuel injected engine.

So you need to keep it rich when cold by either tickling a bit more, doing a second tickle after it starts, and/or adding back in the carb chokes if they have been removed and using them.

You likely also have worn slides, so as long as the carb bodies have also not worn as badly you can fit new anodized slides and reduce both air leaks and the rate of future wear.

I put my helmet and gloves on first and then I can use the throttle to keep the bike running until I get onto the tarmac 400m later and then it will be warm enough for a reliable idle.

I also have a Digital red box Boyer, this has an idle stabilisation advance curve, as the revs drop below 900 the ignition advances and the revs rise back up.

32mm carbs are only needed for Combats and 850's, not std 750's.

John's advice is good, but I've discovered that after tuning the idle as per the normal method I find that if you then set the mixture screws a touch richer than need be you get a more stable idle with a hot or cold motor.

I usually adjust the mixture screws in a further 1/8 to a 1/4 turns from the normal optimal setting and then re-adjust the idle screws to suit . 

500 to 600 rpm idle is then possible.

Short video of warm up idle:-

https://photos.app.goo.gl/Fj3qxetqkvBhuDH69

Good luck!

Ultra-slow idle speeds may confer fun bragging rights, but I'm not convinced that they're a good idea. In his new book Norman White suggests 800 rpm.

On a different note, if Stephen finds any traces of dirt, encrusted deposits, etc, in his carbs a trip through an ultrasonic cleaning bath is recommended — did wonders for my Amals.

(To the best of my knowledge these latter are veterans from 1972; when I first got the bike it ran absolutely terribly on moderate throttle openings, cured with new needles, needle jets and anodised slides. A subsequent problem with starting and warm-up was cured by the ultrasonic treatment.)