Small Engines (Lawn Mowers, etc.): Briggs engine mixture adjust, carburator, fuel feed

Question
Briggs 12.5 HP IC 286707 engine runs rough at higher speeds.  Idle mixture sets up fine and engine idles real smooth.  Can't seem to find a high speed mixture adjustment.  Original problem was the fuel feed tube from the bowl to the venturi was plugged.  A small wire remove the debris.  Some carbs have a hi speed mixture adjust screw on the bottom of the bowl but this one just has the small stud to hold the bowl on.  Is it possible the OHV valves need adjusting.  I did not check this.  Engine starts good. Thanks  

Answer
 Hello Hal:

 It could be the Valves. I Set all the Valves at .013in Intake and .017in Exhaust. Did you Soak the Carburator in Cleaning Solution to Remove the Varnish from Inside the Carburator Passages? Most of the Time if the Carburator is Not Soaked the Varnish that Gas Forms Over Time will Still Restrict the Flow of Gas to the Jet and Cause the Problem you Described.