trouble getting steady idle under 2000

Ok, after lots of riding and lots of fun, I got to thinking about this again and before trying the old fashioned synch I decided to try the old starting fluid test again. Absolutely no change in rpms anywhere except where the right carb boot attaches to the airbox. But riddle me this Batman, I didn't get an increase like I would expect what I got was: the engine died. Repeated several times, so its unmistakably happening. I got a slow down once on the left boot, but could not repeat it so I'm not certain there.

I suppose I should look at the plugs now that I have a few hundred miles of fun under my wheels and see if they tell me anything