The shorting out the plugs has nothing to do with mixture. It is to balance the two sides by seeing that they fire evenly. It is for adjusting the idle speed. You now have dual plugged heads and would need some elaborate set up to use this method of balancing the carbs. That has been done but I think with limited results. You can also balance the carbs on just the top plugs which might work. Your best bet is finding or making a carb balancing tool. The Harmonizer has been popular lately but is out of production, it might be back, someday.
After you have changed all the oils, and adjusted the valves, and put in new plugs, what kind of ignition is this bike running(?) Stock is just points but as SS says you should have a booster.
I think my Beemer idles better if the mixture is on the rich side.