Johnson Controls Parts What's This Little Button On My 8.0 Hp Johnson Outboard?

What's this little button on my 8.0 hp Johnson Outboard? - johnson controls parts

I have a mid 80 Johnson 8 hp outboard, and there's this little button that part of the button will kill at the end of the address / control arm threaded screw on the outside. Is that something caused the gas that the voltage does not work properly to keep the speed of the engine. If so, we need gas, until the desired speed and press the button, right? If someone can help
Jib