My 1976 yamaha yz125 will not ideal and will not t6ake off and a stand still but i can push it and it will go can u help me find out whats wrong please

Start by cleaning the carb inside and outside and also clean the air filter. Check for cracks in the reed valve and mounting joint rubber. This is the stuff between the carb and the cylinder. Be sure the battery is in good condition. Now stick in a new spark plug, NGK BR9EIX. Next, remove the left side case, (shift lever side ), and clean up any rust on the rotor magnets and pulser coil. Put in some fresh gas. Parts can still get parts at the site below. Don't use the "Quick parts look up", instead use the "Parts search by model". This will then let you see entire parts assemblys. www.babbittsonline.com