1) those small washers and pins often come in a carb rebuild kit, which you should always have one or two on hand.
B) hesitation/stutter under load at 2800-3k rpm would make me think fuel delivery (starvation) problem maybe...or timing(needs more advance?)
III) i never tach mine that high until...
I always thought that was called the throttle positioner, and somehow slowed the closing of the throttle when you took your foot off the skinny pedal.
Obviously, i don't understand it and i fear what i don't understand. So i just took mine off. Probably didn't work anyway.
Looks better without...