ok the problem is the centrifugal clutch springs are either broken or stretched,more than likely broken though this means the clutch is engaged when it should be held from engaging by the springs until sufficient revs are achivd to pull away.put some new spring on and it will be ok these are as tough as nails to fit though,to get some cheaper than honda try ve-uk online they will supply you with some good stuff.
adam bike doctor, April 2010