since mercury has made outboard motors from 1.5hp to 600hp ranging from single cylinder motors to 12 cylinder motors and over the past 85 plus years.
would help us to know what you are working on.
'kogs, you may have been clueless about sterndrives, however you were mechanically inclined. the OP stated they were noobs at boats and having little mechanical ability. there is a difference.
I do agree the stringer is a great drive for simply puttering along at idle.
its not your coil
its almost never the coil and the fact that your engine is running proves its not the coil.
what is your fuel pressure?
how did you "check" the fuel filter? they are a one-time use filter
with only 18hp.... pull a hydrostatic transmission from a riding lawn mower.
use a spline coupler to couple to a prop shaft.
you do have to keep the lawnmower transmission mounted pulley up.
then you have forward and reverse and neutral.
however to go thru all that work and cost. a used...
I would machine the mounting boss and drill the hole myself
or if you go down the e-pump path, get the oil switch and relays to wire it properly.
no return line needed. pump doesnt over-take the float/needle
for about 2 months the skyway causeway caused my allergies to flare as the smell was horrendous. The beaches in Manatee and Sarasota are suffering as well as the Pinellas beaches.