Small Engines (Lawn Mowers, etc.): Old 8HP B&S, briggs and stratton, hp briggs

Question
Hey Marc-

I've been tinkering with an older (mid-'80s) 8 hp Briggs and Stratton on the back of a Snapper rear engine rider and I am currently having trouble getting it to idle properly.  

I've done just about everything to it except take off the head (replaced the blower case on top, new oil, new air filter, new fuel & filter, removed the carb and thoroughly cleaned it, new plug etc..).  Now it starts up fine and runs pretty well at full throttle, but not sure of the best method to getting it fine tuned so that I can throw the throttle back without it dieing.  I've been playing around with the high end adjustment (bottom of the fuel bowl), the adjustment screw on top of the carb (above the bowl), and the idle screw on the side of the throttle plate, but just not getting it to come into a nice tune.

I have an older Clinton's small engine book which suggests setting the two main adjustment screws all the way in then back a turn & 1/2, getting it warmed up and set on 3000 rpms (not sure about that because I don't have an rpm guage), then starting with the high end move it to the mid point between lean & rich sounds, then to the same with the idle screw- what it does not mention (becuase the book is pre-my carb date- book print was late '70s), is how to incorporate the screw on top of the carb above the bowl (is that an alternate idle screw or what?).

Thanks for your advice- do you think I should go ahead and remove the head - adjust valves and replace the gasket, or do you think it is just a matter of proper screw adjustment?

thanks-
Philip

Answer
1 1/2 turns out from lightly seated is, in general, a good starting point for these mixture screws.  The high speed mixture (bottom of bowl) should be then adjusted in until the engine starts to surge a bit and then opened 1/4 of a turn.  The low speed mixture (top of carb) should be adjusted only open enough that the engine doesn't stumble when you go from idle to full throttle abruptly.  Then you would set the idle speed with that screw and re-check the low speed mixture screw setting again.  I can't think of any reason to remove the head unless you think you have a compression issue.  Hope this helps.