Small Engines (Lawn Mowers, etc.): Briggs carb adjustment, ohv, great dane

Question
Hi Michael,
I have an 18hp Briggs Vanguard twin OHV on a Great Dane Super Surfer that is four years old (~140 hours).  Over time, it appears that the carb is running a little rich and has begun smoking under load.  I replaced the air filter and that helped a little, but it still seems to be running a little rich and sluggish.  Finally my question: How difficult is it to adjust the mixture and is there a schmatic available online that shows the carb layout?  Also, do you have any other ideas as to the cause of the issue?  Thanks for your time,
Henry

Answer
Hi Henry,

Try adjusting the mixture screws.  I don't know of a schematic except ordering one online from B&S.

The high speed mixture screw is initially set at 1 & 1/2 turns out.  Then adjust it to give good acceleration and top speed, while not closing the screw more than you need to.  The low speed mixture screw is set at 3/4 of a turn out.  Adjust that, to give a smooth idle.  The 3rd screw, the idle speed screw, is set to give a low idle speed without stalling.   

Let me know how you make out.
Michael