Sometimes it's the simple stuff.
I installed the stock carburetor. Problem solved. No more irritating little glitch at light load. In the process of setting up the stock carb for the modified engine, I reviewed some articles on the Mikuni CV. I found a pretty good rundown from an outfit called Factory Pro. They use the float level to tune light load conditions. I found that interesting.
Since it ran fine with the stock carburetor, I figured my problem must be the S&S carburetor. Its not the exhaust header or the new hi-flo air filter. That float level thing kept grinding at me. I checked the level several times. It was exactly on the S&S spec, but that spec is for a big V-twin. I'm runnin it on a 40 inch single.
I readjusted the float level to 1/16" above the S&S spec. End of problem. Now it responded well to tuning and in no time flat it was runnin better than ever.
I am amazed at how well the thing responded to such a minor adjustment. It makes perfect sense. The idle & transition circuits were designed for a much larger engine that pulls a lot more manifold vacuum. The little Savage mill with the big cam just didn't have the oomph to lift that fuel up into the low speed circuit when the throttle plate was in the final stage of transition. Raise the fuel level and it doesn't have to lift as far.
If you are interested in a pretty good step-by-step for tuning the stock Mikuni CV, check out this Factory Pro link. It's got some good stuff in there. You learn something new every day.
http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_...