shaking under throttle at higher speeds

Mini Bike & Go-Kart Parts

So like the title says, i noticed under heavy acceleration nearing top speed there's some heavy vibration so badly i can feel it through my entire body and have to let off the throttle and slow down, slower speeds & light acceleration are smooth though. I'm thinking some rubber motor mounts might be a place to start but then there might be some clearance issues with the frame and 212cc motor/gas tank. Any thoughts??
Try this

You may start throwing chains if you use rubber under the motor. Your motor plate is flexing, the adjustment slots weaken the plate. Place one washer on top of the plate and one under the plate on each mount bolt, continue to use the standard washer on the bottom side as well. this will work on a four slot plate. For a six or eight slot plate you will need to be more aggressive with your stiffinin'. For these you need 3/16" X 1 1/4" strap
Cut to fit in between the frame under the motor plate frame to frame. Drill holes for the bolts to fit through. The stiffest is a plate top and bottom, large area washer top and plate bottom is next. Just better is motor top with plate on the bottom. I just use mcmaster for reference only, you can source you product from any place.

Hope that helps good luck
Hmm never thought it could be simple as a few oversized washers ill give that a try. Previous owner just bolted the 212 right onto the engine plate that is welded to the frame so its only four bolts