Well when its higher rpm like 2500 holding it there it stabilizes pretty good, then when you let off it snaps up real quick then recovers pretty quick too,, the valves may be a problem and it was a weekend cruiser now it has to be a daily driver soon, so I am trying everything I can, I guess a midrange vibration could be that the transition in the carb leaning out? I have a 6.5 power valve in it right now, Ill check it all out tonight pull the carb 100% down and go back again, see if Im missing something. I just didnt think a vacum issue due to having decent power brakes, lol, but could suggest why when I put my foot on the brakes the idle would go up about 75rpm, ??? new theroy I guess.