Small Engines (Lawn Mowers, etc.): Setting Idle and Speed, briggs and stratton, hp briggs

Question
I just replaced the blown engine on my Allis Chalmers T-816 garden tractor.  I went from the old 16 HP Briggs and Stratton to a newer (not brand new) 18 HP Briggs and Stratton - I/C #422700.  Doing this was a serious stretch of my comfort and skill levels, but I felt it would be much easier for me than rebuilding the old engine.  I think I'm close to declaring victory, but one last thing has me VERY frustrated.  I can't get the idle right.  

Before sending all my hard work bounding down the hill out back, in a fit of tractor rage, I thought I see if an expert can help.   I've been adjusting the Idle Mixture screw on the front of the carb, while also adjusting the Idle Speed Screw on the side of the carb.  I had it at a point were it would idle and run while in gear, but it was obviously too slow and there was little difference between 1st and 3rd gear.  Now it's at a point were I think the idle RPM's are close to right (but how do I know, I'm going by sound?), but when I put it into gear it immediately stalls.  I don't think this is a safety switch problem because I was able to run it in gear under my previous adjustment, and I think the previous owner bypassed at least the seat safety switch (if it had one).  So, there is a brief history (trust me), and now my question:  Is there a baseline setting for both of these screws where I can start and then systematically make adjustments to get it right?  Right now I feel like a chimp with a screwdriver.  I think the Idle Speed Screw is my bigger hurdle. I did find the owner's manual online, with pictures of the screws I'm talking about - http://www.briggsandstratton.com/om/pdfs/100/274796-Domestic.pdf

Thanks!  

Answer
Hi Barry,

The idle mixture screw is critical, where as the idle speed screw is not.  The mixture screw is initially set at 3/4 of a turn out.  Adjust it to give a smooth idle.  I assume that there is no high speed mixture screw?  If there is, I think that is the problem.  Set that at 1&1/2 turns out and adjust if and as needed.  To set the idle speed exactly, you would need a handheld tach but I would just the speed for good performance.

Let me know how you make out.
Michael