very basic  magneto to service…

try a new plug on the cold cyl.

measure ohms from plug boot to engine frame   xpect 4-8kohms if coil is not defective

when was the magneto serviced  to inspect for cracked coils bad condensers dirty points   etc… lot of info available if you want to jump in and fix it free  instead of paying $100/h  plus parts…….. lots of help here  and your only costs will be available parts if needed.

This could be as simple as cleaning the points associated with the bad cyl…  front coil feeds the top cyl !!

here are a few docs to read plus you have tons of utubes to fix  magnetos used from early 50s to late 60s    print this manul

https://www.aomci.org/wp-content/uploads/attachments/1972%20Evinrude%209.5HP%20Service%20Manual.pdf

this bible on “older” motors covers magnetos extensively plus lots of outboard  concepts to learn

https://watercraftmanuals.com/outboard/johnson/johnson-302231.htm

visit Leroy’S tech info.. covers magneto concepts, repairs .. 9.5hp etc..   print what you need !   see the 9.5hp MQ series

OMC outboard related articles

shop repair/time  may cost more than the engine value !   ….why not give it a try.   a lot of times it is only a cheap part like a condenser or dirty points.

https://youtu.be/JOPJK3Foan0