I had that same engine in Johnson clothes and went thru the carbs for the first time last year. Pretty simple design. Tore down, shot carb cleaner thru the passages followed compressed, filtered air and reassembled using the original parts. A little wear shone on one float valve. I was surprised as to how clean the bowls were, but I do use an external filter. Found no gum or varnish. The old dealer told me a long time ago how to prep it for non-use. I do this even if it is just setting up for a week.
He said, run the engine on the hose until at least warm at idle. While still running, disconnect the fuel hose. As the fuel begins to run out, the engine will start to rev up on its own. At that moment, choke the engine until it stops and turn off the key. This leaves the bowls mostly empty and the choking leaves a rich oil film in the engine. It has worked for me and the engine has never had any power head issues.
However, wear over the years had dropped the compression to about 90 psi. I could never find any definitive compression spec, and I had the service manual and had asked the dealer.
The Preston Tilt/Trim was getting weak and the internal relay would click out every few seconds. Only other $$ spent were on regular replacing of the water pump, occasional drive shaft seals and about 3 years ago having the prop shaft resealed.
Overall a great enging that never left me stranded or refused to start, except for my own fault. I did have to rope start it once when the starter solenoid went out during an outing. But it only took one pull.
Might add it is a saltwater baby. Though it was replaced last year with an ETEC, I retain its picture on my avatar.
The old Johnnie would push the 18" trihull at 40 mph. Anxious to hear how yours performs.