check the valve clearances they always go tight on these chinese scooters as the metal is soft and they recess in the cylinder head.if you cant do it properly get someone who can to do it for you properly.must be set on top dead centre on the compression stroke.inlet .05-.08mm exhaust .08-.12mm the exhasut is the likley culprit but check both.i see this problem very often trust me its very likley to be this.
adam bike doctor, February 2010
