Small Engines (Lawn Mowers, etc.): engine surging, briggs surging

Question
my bolens mower with 4.5 brigs eng. will not hold rpm starts fine runs ok but constant up and down of rpm. no weeds in governor links, good plug. Ignition??

Answer
If this has the plastic carburetor mounted on the fuel tank, it may be in need of replacing.  In the past I have replaced maybe half a dozen a year.  We've already replaced that many in the past 6 weeks.  I think it's from the ethanol in our gas as it's known to be rough on some types of rubber and plastic, but I can't say for sure.

What you should try first is cleaning the carb and replacing the diaphragm if this is the carb you have.  You can use spray cleaner and a fine wire to clean it.  Be sure to replace the mesh screen that's on the fuel nozzle pick-up, (The short pick-up tube) and the O-ring between the carb and intake.

Let me know if this isn't the carb set-up you have or if this doesn't fix things.  Thanks, PK.