1993 yamaha jog scooter will crank but it wont accelerate?

I was riding in the rain today going about 35mph. And suddenly the scooter slowly bogged out. It cranks right first time every time but when both wheeled are on the ground when you try and accelerate you go no where slight smoke comes the exaust its a 2 stroke but its almost like the horse power just stopped. When the scooter is ok the kickstand and the back wheel is off the ground the wheel will turn very fast when excellerating. But when its on the ground it won't budge. How can I make my scooter go again?