Re: Johson 8hp idle problem
If you're talking about the slow speed adjustment, you'll find the knob on the tip of the tiller handle. Clockwise will speed the engine up. Counter-clockwise will slow it down. It's designed for use while trolling, to make fine adjustments in the engine speed.
There is an idle stop adjustment on the carburetor as well. With the throttle at its lowest setting and the slow speed knob turned fully counter-clockwise, you can adjust that screw to the minimum speed that allows the engine to run smoothly in gear. It's on the side of the carburetor.
The idle mixture screw, which controls the air:fuel mixture at idle is on top of the carburetor. You may be a bit rich on that one. Clockwise to lean out the engine at idle. Counter-clockwise to richen it. Adjust this in small increments (1/8 turn), then wait for the engine to adapt to the new adjustment. At some point, as you go lean, the engine will speed up a bit. A little further, and it'll cough or sneeze. Back the needle out 1/8 of a turn at that point and you'll be good to go.
The combination of those two adjustments should give you an idle, in gear, that lets the engine just putt along. When you get it right, you'll be amazed at how slow you can idle.