I just bought an older Johnson 18hp, pervious woner said everything
works except maybe have to play ard with the choke when starts, but
when I got there to collect it, he told me it will start but dies
almost immediately unless u throttle it a little or full, it runs real
good when it's in gear(with throttle)...it only dies when u switch to
neutral(before switching to forward or reverse), so the only trick is
to switch to neutral real fast while the other hand switch the gear and
throttle almost at the same time to keep the engine running. Below are
the owner's "mechanic" recommendation, but I am starting to think he
knows nothing much, otherwise he would have fixed it then.

1.) Coil problem - not sure if it's going to be an expensive fix if it
is true.
2.) Clean Carb - but he said he rebuilt the carb previously, so I was
wondering how come it's cleaning when it's been rebuilt recently.
Engine has been tuned up recently too, maybe that's why it's running
great, but don't know why it won't continue to idle properly.
3.) He recommended using something called "Restore" to clean the
carb....couldn't find it in store, anyone knows what he is talking
about?
4.) there is a knob in the middle, between the choke and the STOP
button...he doesn't know what it is, neither do I, but I am guessing
it's the fuel mixture/ For LEAN or POWER up??? COuld that be the
problem? We did not touch that knob throughout the whole testing...the
motor just keep dying if you don't get the "switch fast" method
correctly.

Any expert recommendation how to fix this before I bring it to the
mechanic for them to chop my head off?

Regards,
1st time boat owner
Ron