Here's an alternative method to setting the idle mixture. Set the idle mixture so that you get best acceleration from idle to 1/3rd throttle when you jam the stick from idle to 1/3rd. Diaphragm carbs don't have accelerator pumps. Setting the idle mixture for crisp acceleration results in a slightly rich mixture at idle, not too lean and won't flame out at a bad time. If you set the idle mixture too lean, you can easily hear the motor gasp as you do the acceleration test. If the idle is set too rich, the acceleration is slow and the engine will blubber until it clears the mixture.