Small Engines (Lawn Mowers, etc.): Lawnboy Model S21ZSN, exhaust ports, self propelled mower

Question
My 1989/90 Lawnboy Model S21ZSN self propelled mower runs but  slowly and doesn't have enough power to use the self propel feature. I've changed the plug, cleaned the filter and added 2 cycle engine tuneup additive. Next is cleaning the exhaust ports. But I'm thinking I need to adjust the throttle or carb. Any help with these would be appreciated.

Answer
I would first examine the exhaust ports and muffler before you start adjusting the carb.  It's unlikely the carb adjustment has changed anyway (or enough to cause a total loss of power).  Also examine the piston and rings for scoring once you have the muffler off.  Hope this helps.