Thanks to everyone who contributed to this thread.
Just fixed a problem related to those pesky vacuum caps - no idle at normal idle speed, left carb popping, and backfiring from left exhaust. The cap closest to the engine on the left side was gone except for a dry rotted ring of rubber.
Replaced the cap, no popping, idle normal, spares in my saddle bag. Ready to ride to Indy for the Moto GP. Life is good.
