Small Engines (Lawn Mowers, etc.): Toro Lawn Mower Surging, internal passages, carburator

Question
Marc, I have a 1988 Toro OHV GTS Model 20620 lawn mower that surges at idle/low speed. Runs good at higher RPM's. Keep air filter clean,spark plugs,oil changes,wheels lubed,regularly. No other maintenance has been required. I notice the lever that is attached to a shaft that enters the engine casing in the rear, and is attached to the throttle on carburator, is some sort of a govenor? that is varying the throttle idle speed (surging). Do you know the cause of the surging? Thanks, Jerry

Answer
This indicates there is either a blockage or an adjustment to the low speed mixture screw is required (if equipped).  If it has an idle mixture screw, try opening it 1/8 of a turn at a time until the surging stops.  If this doesn't correct the problem or there is no low speed mixture screw, the carb needs to be cleaned thoroughly, including pushing a piece of tag wire through all of the internal passages and following up with aerosol carb cleaner.  The governor is doing exactly what it's supposed to.  Hope this helps.