Brian a workshop manual and not a owners manual will tell u every adjustment on the engine in fine details, look up carburetor in the powerhead or fuel section than goto the spec's section look at "mixture screw" or "air idle adjustment" it will have a number this corresponds to how many turns out the screw should be after seating it
if u have high or low mixture screws on a carburetor usually the high screws are higher on the carburetor than than low mixer screws
if u have high and low mixture screws your in a bit of shit without a test tank because the high mixture screw u must have the engine going top speed u than shut off the engine and read the spark plug a bit hard if your in a river, if u power the boat back to the ramp u will get incorrect readings