Re: Reducing Vibrations at High Speeds.
I cut the stock hard grip off the throttle and replace both grips BMX foam grips on most every build.
Pull the throttle barrel out, cut off the grip, cut your foam grip to length and soak it in some hot soapy water and then just force it on with a kind of 'milking' action.
Foam grips are a pleasure to ride with.
A good front mount helps too, sick bikes has them, just measure your downtube so you get the right sized one.