1954 18 hp Johnson Seahorse

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Vstardude

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HI Everyone, I have a 1954 18 hp Johnson Seahorse. The motor runs pretty good, it was my grandpa's and I have had it for about 5 years, but the spark plugs keep fouling up. any ideas on why and what I can do to fix it?

Thanks for the help
 
I am using a 50:1 gas mixture. I thought it might be that, but I read a post on here a few weeks ago that said to use 32:1 because of how the gas has changed in the last 50 years.

For the spark plugs, I am using champion j6c.

Thanks for the help
 
First off, the engine is later than 1954...that's a plus! Johnson made the 18hp starting in 1957. Second, no matter what a local mechanic tells you about how much better todays oils are than "way back then" the engine needs at least a 24:1 fuel/oil mixture to live a good long life. Added benefits of the mixture are better internal sealing, less piston skirt wear, plus numerous other benefits. Todays oils will smoke less than the old oils as well so do it right! You absolutely will not foul plugs on this mixture if your ignition system is in good condition and you have the right carburetor setting in a good functional carburetor. Flooding or leaking carbs can foul plugs as well as weak or cracked coils, dirty points, condensor starting to fail, etc. can give you a misfire similar to that of a fouled plug. Give us a service history of the engine if you can and we can guide you in the right direction.
 
Well I don't really have a history. I know it has been kept inside every year during the winter. I remember when I was young we used to have trouble with it almost every time we went out. About 15 years ago the gas tank fell apart when my dad was changing the gasket and ruined probably the best walleye fishing we have ever seen (6 of them in 45 minnutes, all 20-26 inches long in lake superior) I know my dad had a lot of the wiring redone in the 90's and it runs pretty good. There is an electric start, but I don't need it so I took the wires out of the boat, although there is still a starter in the motor. If it has new plugs in it, it will start on the 1st or 2nd pull every time. I did just find some repair orders that say it had a carb kit done, new plug wires (only one was working) and fuel line test done in 97. Since that time it has had no more than 50 hours on it.
 
first i'd make sure both cylinders have a nice blue spark. if you have a spark meter that would be even better

once you rule out the ign. system we'll know its running rich and you can start diag'ing the carb
 
So the carb kit was done 13 years ago. In that time it has sat dry numerous times and had a chance to varnish up pretty well. On top of that I am assuming you are running alcohol extended gasoline. Unless the gasket between the carb bowl and body is a light brownish color that kit does not have a great ability to resist alcohol fuel. I believe there is a good chance your needle and seat leaks a little. Lets say for right now that it does not and try a couple simple things. Before starting the engine. Adjust the High speed needle by turning it in until it closes (gently) and then open it 3/4 turn and leave it there for now. Now start the engine and let it warm a little. Adjust your low speed needle clockwise (slowwwly!) until the engine runs at its best idle and highest idle RPM then begins to sag and slow down. Stop there and go the other way until you get the highest idle and then go another 1/8 - 1/4 turn out. Run your engine now and get it up to high speed. Turn your High speed needle in or clockwise until you reach the highest RPM and keep going slowly until the engine slows down. Quickly return to the highest RPM position and go another 1/8 turn or so counter clockwise to give it a little more fuel and oil. From this point, if your ignition system is good and your carb is not leaking you should not foul spark plugs. You can routinely run these engines on as much as a 16:1 fuel/oil ratio without fouling a plug.
On your ignition system. With the plugs removed you should be able to jump a 1/4" gap by pulling the engine through with the manual starter.
 
Loggerhead Mike said:
first i'd make sure both cylinders have a nice blue spark. if you have a spark meter that would be even better

once you rule out the ign. system we'll know its running rich and you can start diag'ing the carb
Click to expand...


I do have a spark meter and they both work great, i even got a little shock when I was testing them!!!
 
Pappy said:
So the carb kit was done 13 years ago. In that time it has sat dry numerous times and had a chance to varnish up pretty well. On top of that I am assuming you are running alcohol extended gasoline. Unless the gasket between the carb bowl and body is a light brownish color that kit does not have a great ability to resist alcohol fuel. I believe there is a good chance your needle and seat leaks a little. Lets say for right now that it does not and try a couple simple things. Before starting the engine. Adjust the High speed needle by turning it in until it closes (gently) and then open it 3/4 turn and leave it there for now. Now start the engine and let it warm a little. Adjust your low speed needle clockwise (slowwwly!) until the engine runs at its best idle and highest idle RPM then begins to sag and slow down. Stop there and go the other way until you get the highest idle and then go another 1/8 - 1/4 turn out. Run your engine now and get it up to high speed. Turn your High speed needle in or clockwise until you reach the highest RPM and keep going slowly until the engine slows down. Quickly return to the highest RPM position and go another 1/8 turn or so counter clockwise to give it a little more fuel and oil. From this point, if your ignition system is good and your carb is not leaking you should not foul spark plugs. You can routinely run these engines on as much as a 16:1 fuel/oil ratio without fouling a plug.
On your ignition system. With the plugs removed you should be able to jump a 1/4" gap by pulling the engine through with the manual starter.
Click to expand...

Vstardude,

Pappy, has given you some excellent advice!!!! =D>
 
Hi Pappy, I went out last night for about 3 horus and I didnt do exactly what you said because I couldnt remember exactly what you said, but I did play with the high and low speed needles and today they werent plugged at all, and it started on the first try. Thank you so much for all of your help


-Vstar
 

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