Small Engines (Lawn Mowers, etc.): briggs & stratton engine 4.0 hp, briggs stratton engine, briggs stratton

Question
The engine seems to go up and down in speed. Is alternates every couple seconds.  
Same rhythm.  I tried changing air filter and got a new spark plug. Also uses more gas- probably twice as much to do same job.  

Answer
 Hello Jerry:

 From your Description I suggest the Carburator be Cleaned and Rebuilt. The Carburator Jet is Restricted by Varnish that the Gas Forms over Time or the Carburator has Drawn Trash/Water into the Jet. If you need a Breakdown of the Engine and Carburator, Send me the Model, Type and Code Numbers Off of the Engine, Please. With these Numbers I can Locate a Breakdown for you to View Online. Hope this Helps. I am here if you Require more Asssitance. Let me know what Happens, Please. I enjoy knowing the Outcome. Thanks.

 Good Luck

 Respectfully

 John