When I am running at mostly a constant speed at 40mph-80mph I occasionally her a a "psst cha" with some surging.
I recently changed out my box filter to a chrome spike air filter. i ran into an issue that had the tip of the spike resting on the highway bars. I adjusted the bracket that the spike came with and solved the problem, but it tilted the carb up. I also placed 2 shims on on the needle for carb adjustement. i have been folling with the A/F screw with minimal success of the problem.
Hyothesis: I think it may be a vaccum leak due to the tilted carb. I may need to fine tune the A/F screw.