Re: 4.5 hp Mercury carb problems
Ron, about the only screw I can think of to adjust on the carb itself would be the idle mixture screw. The main jet is fixed so you can't do anything with that.
To get a very rough setting on your idle mix, lightly seat the needle (fully clockwise) then back out approx 1-5/8 turns. This should be close enough to get 'er started.
These Little Ones don't flow a lot of air or fuel so they're quite touchy on the mixture adjustment, make small changes on the mixture needle and let things settle out for 15-20 seconds before 'tweaking' on it more.
Adjust for smoothest/fastest idle, if it gets cranky on the re-start or is overly cranky when cold, richen the mixture (CCW) 1/16-1/8 turn.
Note: if you need to adjust the idle speed, use the Throttle Stop screw. It's the one with a locknut upon which the throttle linkage rests at Dead Idle.
Don't mess with the Spark Advance/Stop screw, which is the one that limits the travel of the linkage at Full Throttle.
HTH..........ed
