Re: Slow Speed 2-stroke 66CC
I'm no real expert, I have only built 3 kits but if I had to bet I'd say your problem is in the carb.
Please don't assume that " brand new out of the box " means everything is OK. Obviously it is not. You should be doing 50 KPH easy.
Check the choke first. The boygofast kit I bought didn't even mention the choke in the instructions. If there is not a choke cable then there is probably a little lever right behind the air filter. Up is closed and down is open. You want it closed to start it when cold and open to let more air into the engine.
The kits that give you a carb unassembled are easy to put together wrong and the one kit I got that came with the carb pre-assembled was put together wrong. (It almost worked right and I didn't find the problem till I took it apart to find out why it kept flooding.)
Make sure that cylinder inside it is going up when you turn the throttle. That's what lets the gas/air mix into the engine.
If you have to take it apart be slow, patient and careful. Above all don't lose any of those tiny little parts.