Snowman -

Tom's procedure is pretty good and should help you make progress.

Once you set the idle mixture screw to where the motor runs decently leave it alone and get your timing squared away - then adjust the idle speed screw for optimum idle speed and double check timing.

You should have no problem getting a 500 - 600 rpm idle speed unless you have a really lumpy cam and the motor will shut down nicely with the idle speed set this low.