1959 Johnson 2 cycle 18 hp motor compression

I bought a 14-foot Aluminum StarCraft with an F-13 Johnson 18-hp 2-cycle motor. The seller says it ran this spring. I changed the lower-end grease and no apparent leaks. The grease was clean and the right color. I have not been able to get it to fire on new gas.

Spark parks look dry so it could be carburetor issues. The gas tank pumps up pressure fine.

The motor does not fire on a touch of sprayed ether in one cylinder. The spark seemed weak when I pulled and grounded the plug. The points, condenser, and magneto have not been checked yet.

I just checked the compression on both cylinders. Cold and dry cylinders. 71 psi on each cylinder.

Low but runnable?

I want to get your opinions before I invest money and time in new plugs, points, and condensers and a carb clean/rebuild. Is the motor worth it?

The current spark plugs are Champion J8C. I believe the OEM calls for cooler plugs. J4C. Should I go with a 4, 6, or 8 heat range? NGK plug instead?

I am not panicking. The boat came with a Mini Kota 35 lb Power Drive and I have a 52 lb Mini Kota 12 volt also. It would be nice to have the 18 hp to save some travel time on the Castle Rock Lake in Wisconsin. I am hoping to land some nice Channel Cats for the smoker.

Thanks for reading

Usually a lower compression motor will run so long as both are even psi, but you may have issues running when the back pressure increases wen in the water.

I've had viable motors down to 55 psi but they lacked power.

Most 18hp motors I've had were well over 100psi. some as high as 190 psi and so hard to pull they broke ropes.

Thank you free,,, and pappy. I am moving into new house the 26th. So I will work on engine after the move. Oil/gas ratio will be done with some Seafoam. Have a carb kit coming. Ignition system spark tester is here.

I have experience working on sytems with points. Retired farmer. I am looking forward to troubleshooting. Will report my experience.