no you cannot adjust the timing it is set in the cdi unit,the only way it can slip is if the woodruff key that holds the magneto in the right position on the crankshaft shears in half.i would suspect a blocked up exhaust pipe or possibly a blocked air filter these are the main reasons that an engine will not rev out.does it idle/tickover ok or do you have to keep it running by twisting the throttle?
adam bike doctor
October 2006