1972 Johnson 9.5 model 9R-72 L

Hi
I just boat a 9.5 HP model 9R72L, the motor runs fine but the idle is a bit high. I noticed that the throttle handle does not return all the way back to the STOP position. I opened the cover and also noticed that the piece of metal, connected to the throttle hanle, that slides back and forth to open and close the throttle does not slide all the way to loose contact with the throttle arm from the carb. I'm not very familiar with outboards or their terms so please excuse me!

Is there an adjustment to the throttle handle? Any other solutions?
Also before I fired it up in the barrel, I drained the lower unit and refilled it, tightened the screws and wiped all the oil but when I ran it for 10 minutes, I noticed a fair amount of black stuff floating in the barrel. This motor has not been run in a couple of years, is this something to worry about?
Thank for your help

Not sure about the first question.

On the second, what you saw is unburned oil/gas mix & carbon from the exhaust system. Normal for a 2 stroke, even new ones.
If the oil was from the lower unit, it would not be black.