Mudge,
I have the same setup on my daily driver. Sounds like the throttle shafts may be worn, which would cause both an air leak and an unpredictable throttle return. Disconnect the linkages and feel for play. Also, pull off the tops of the carbs (5 screws I believe (and you'll have to pull out the pin that holds the linkage to the choke butterflies) and look for crud in the float bowls. If you pull the tops off carefully, you can re-use the gaskets. This will also be a good opportunity to write down all your jet sizes.
The primary and secondary fuel jets sit in the bottom of the float bowls, which is exactly where the crud collects, that may be causing some of your problems. The air filter base holes are for the valve cover breather. I have mine connected to one of the carbs, and the other carb, I blocked off the hole.
HTH,
Tim