I don't like 30 seconds. Make these adjustments in quiet area and just listen, don't make adjustment until you hear the last .
I owned 20 hp Johnston, a 60 and 2 175's of this erea. These are carbureted engines means I'm old. Most important with all these carb Johnston is have the motor trimmed level on initial start.
My 175 rude I traded in, 6 months later I went to Green Bay Wisconsin and one of the other guys has my 175 rude on same boat. This guy starts talking to me on how hard it was to start. First morning of practice Todd was cranking and cranking motor , I told him to trim it down started. Met him next morning and went threw starting procedure. Todd was flabbergasted how well it started.