Coolster 125cc no first gear. Son has been hard on it. Now he does not have first gear. But all other manual gears with foot selector work. Any one able to help me out with this problem. Thank you.

 

If it is giving an extra neutral where first ought to be, it is almost certain to be a stripped gear in the gearbox. If it jumps out of 1st, it could be a bent selector problem, though could also be worn gear dogs. Either way a partial or full stripdown will be needed.

 

Is there any instructions on how to tear it down.

 

If it has a Honda Cub clone engine, there are lots of U tube videos and on line instructions as to how you strip that engine. Don't get too hung up about the 125 bit as 90cc 110cc and 125cc versions are very similar. However, there are big variations on gearboxes, some have reverse, some don't, some three speed, some four, some single forward and reverse. Try to find instructions for one with similar gears