Small Engines (Lawn Mowers, etc.): Briggs 12 HP Synchro-Balanced on Murray rider -- surging issue, briggs surging

Question
Good Morning, P.K.--
I've inherited a 1990 Murray riding mower with a Briggs 12 HP engine.  When I ride the mower out of my garage, the engine "surges" (rpms change back and forth, high to low).  This causes me to slide back and forth in my seat.  The "model" and "type" code is:  281707 0145 01 90081431
Could I simply adjust the fuel mixture (richer), or would I have to adjust the governor?  I installed new fuel filter, new air filter, new gas, new spark plug, etc., etc.
Many thanks for your reply.   Roger Syrja

Answer
The carburetor needs to be rebuilt and possibly replaced.  This is a very common problem and is usually caused by a gummed up carb.  This is a pretty "loose" carburetor, meaning it can handle some wear and a good bit of abuse.  I think if you clean it in a soak tank and rebuild it with a new carb kit you'll be okay.

Let me know if you have any questions.  Thanks, PK.