4 HP Evinrude from '86
with one carburator.
By the way, I find only one adjusting screw on the carb, where is it
for and how many turns out should it be?

Jan.... The filter is in the gas tank. The fuel hoses may be deteriorating,
allowing debris to enter the carb (check the carb again). The carb adjustments
are as follows:

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.
Start engine and set the rpms to where it just stays running. In segments of
1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the
engine to respond. As you turn the valve in, the rpms will increase. Lower the
rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will
spit back (sounds like a mild backfire). At that point, back out the valve 1/4
turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustment, you will have no reason to move
them again unless the carburetor fouls/gums up from sitting, in which case you
would be required to remove, clean, and rebuild the carburetor anyway.

Joe (30+ Years With OMC)