For info, the illustrated parts list is at http://www.briggsandstratton.com/pdf/illustrated_parts_list/100/MS8142.pdf
This is indeed an old machine - 1984 to be exact.
As a starting point, 1.5 turns out from fully home will allow the engine to be started. To adjust, set speed to full, then adjust high speed screw SLOWLY in both directions to establish the point at which the engine starts to run rough. Set the screw to the mid-point between these two positions. Set the speed to slow, and repeat with the slow speed screw.
Check engine will accelerate smoothly from slow to fast. If it misses when accelerating, back out the slow screw 45 degrees and re-test. The screws may need adjusting slightly, and they are inter-dependant to a small extent.
Adjust the idle stop for a reliable idle. Don't aim too low - the carb (or the engine) is not designed for slow running.
phil_saunders@bigfoot.com
Phil Saunders
October 2008