help with 18 hp Johnson 2 cycle 1959 f-13

[arthurdent]

18 hp Johnson 2 cycle 1959 f-13 on a 14-foot StarCraft Aluminum boat.

The motor does not start or fire on new gas with a light spray of ether. The previous owner said he had it running this spring.

The fuel tank pumps up and fuel comes out the exit of the sediment bulb.
Spark is present, maybe a little weak when the plug is removed and grounded. Champion J8C plugs. Color is good, dry, and gap at 0.03
Lower end gear oil was changed and the color is good with no apparent leaks.
Compression cold and dry cylinders are 71 psi and 70 psi.

What opinion of the compression? Should the engine be retired, or rebuilt? Or get running and live with the current compression?
Is the expense and effort of replacing the ignition set and magneto cleaning a good move without addressing the low compression?
The same question for cleaning and/or rebuilding the carburetor.

During the "fix duration," I have a 35 lb PowerDrive bow mount and a 52 lb Minn Kota transom mount 12-volt trolling motor to augment the oars.

Plugs for this engine? j4c, j6c,or j8c or ngk crossover. What is your favorite?

 

[seahorse]

I've got a 57 FD11 that give me just over 120 psi on a compression test. (J8C Spark plugs)

A buddy runs a '64 18hp that'll break your knuckles trying to start it its got so much compression.

Most two strokes though will start and run down to about 65 psi. Give it a shot of oil and retest and see if the compression jumps up any. If it were mine I'd rather see over 90, maybe even over 100 if its going to be a strong runner.
make sure its able to pull in air when your testing it, and pull it over until it stops gaining pressure, count how many times and do the same on both cylinders.

Since both cylinders are the same, I wouldn't figure its got anything serious going on.

I also won't write off a motor on just a cold compression test without first getting it running first. sometimes the rings are just stuck and a bit of run time will free things up a bit.

I had a 35hp that I bought a parts because some shop told him it had compression left, it had sat for three years on a boat in chicken coop. I oiled up the cylinder, let it soak a bit, cleaned the plugs, made sure it had good spark and got it running in a barrel. I fought me a bit to start but it eventually caught. It was giving me 55/59 psi.

After it ran for about 10 minutes I could here it sounding more stable, it idled better, and started to rev more freely.
When I shut it down, I rechecked the compression and got 110/111. After a few days on the water, and a pair of new plugs is started to really clear out. I checked the compression on it back in March, and its 135/141. Its been on my 14ft boat ever since.

I think it was a bit of it being carboned up, the rings were likely gummed up and a bit stuck as well. I rebuilt the carb, gave it a new water pump, and also cleaned out the exhaust tube and exhaust cover, which I found was all carboned up. After I did all that its been like a new motor again. I suspect the last owner was too heavy on the oil or ran cheap oil. I probably should pull the head and clean it property but its been running so good I haven't bothered.

 

[arthurdent]

TY for your expansive reply! I am going to work with the motor after your response. I have a spark tester coming. Will test the coils. Got a mag puller on the way. And a timing tool for a f-13. Perhaps need a coil template if one is bad.

I found some great youtube vids rebuilding carburetors. So I'll go ahead with that task. hope the lower-end seals are good and the water pump good. Will not know until motor runs.

Such a good fit or the 14' boat I will get the gem working. I did restore a 1949 Panhead Harley back to stock condition. Including rebuild the engine so the concept of the era style engine is in my wheel house. Just a 4 stroke thumper versus 2 stroke.

I am a retired Medical Researcher and a retired farmer (4,000 irrigated acres in Wisconsin). Should be a fun project.

 

[Pappy]

Probably just a set of points that need to be cleaned. Do that before you do much else. As far as compression goes now is not the time to worry. Not all compression gauges are accurate and your numbers are based on a pretty dry engine. Mix should be a 24:1 mix and no leaner on oil....EVER. Your numbers will come up once the engine has been run. Lets start there. You are in Wisconsin? Am currently up in Tomahawk at the largest antique outboard swap meet in the country. Tons of antique and vintage engines here. Look up the meet in the AOMCI section of Facebook if you like.

 

[arthurdent]

Thank you, Pappy. I will do the points and check the condenser and coils. Champion J8C plugs in it currently and will change to new J6C plugs. I am mentally prepared to rebuild the carburetor if needed. Hoping to get the engine going to make the boat top-notch Castle Rock fishing boat.