My scooter shakes when I ride on it. Why?

Yeah everytime I go above 35 mph it starts shaking in a backwards/forwards vibration, not side to side. What does this mean? Is something loose that I'm just not seeing, or do all motorized bikes ride like that?

Lurching;

Possible brake dragging - however that should be noticable at lower sppeds also.
Chain is too loose - can cause lurching as the motor auto shifts
Front steering bearing wornout.

Best bet put bike up on center stand
You will need an assistant
Have the assistant push down on the back of the bike to raise the front tire.
Grab tire and try to move front to back.
If you get a clicking noise the steering bearing may be shot
Spin tire and see if there is excessive drag - if so the brake pad maybe dragging or loose.
Goto the back side of the bike.
Check chain for excess loosness. 1 inch to 1 1/2 inch play at center up and down is the most you need. Tighten if too loose.
Grab back tire try to move front the back.
If loose tighten rear tire nuts and tensioners

Hope this helps
Carl

Its either the tires or the wheels, when tires get low on tread
the bike or scooter will act wierd especially at greater speeds.
The front wheel could be slightly bent not visible to the eye, must
be checked on a balancing device, normally done when mount-
ing a new tire.

maybe the engine has rust inside one of the tubes, so its not pumping properly.

Maybe the problem is with the rider!!!!!

It is trying to buck you off.