'57 Johnson 18hp - Plugs fouling on top cylinder.

[CBGale2]

Any old motor experts on here? Getting this old girl going after years of sitting. Got it to fire up but wont stay running. The engine was missing every now and then, pulled the top plug and it was black, bottom one looked like new. Put a new plug in the top, fired it back up and it ran better for about 15 seconds before it started to miss again, pulled the plug and it was black as the old one. Any suggestions? Fresh gas by the way.

 

[crazymanme2]

Pull a compression test to see where your at.Than check your spark for each cylinder.I believe that motor has points & condenser.

 

[Loggerhead Mike]

take a wire brush to the plug, no need to replace. make sure they are gap'd correctly.

sounds like a weak spark. clean your point contacts and re-set the gap and i bet she'll purrrr

 

[ben2go]

compression test would be good.I believe it to be weak spark.Bad coil or possibly bad points and condenser.Does that motor have dual points?I would do an ignition rebuild,points,condenser,coils,and plugs.Also check the wiring to the points,condenser,and coils for chafing.

 

[CBGale2]

Yes it is dual points and condensors.

 

[Top Cat]

Usually a fuel problem rather than ignition, do you smell fuel when you take the plug out? Even though its a single barrel i believe that motor has 2 low idle adjust screws and just one for fast idle, make sure they are adjusted properly and nothing gummed up/stuck. You may even try a 1 step hotter plug in that cylinder. Be sure compression is good, and you are getting good spark, but focus on fuel first that is usually where the problem is on a fouling plug.

 

[CBGale2]

Single slow speed adjustment on it, nothing really determines how much fuel goes to each individual cyclindar, as far as I can tell. Going to go with the electrical stuff first and give that a try, Ive got a carb kit on the way as well so that will be next on the agenda.

 

[Loggerhead Mike]

the black on your plug is unburned fuel. i dont think something in the electronics failed, since it will run untill the plug fauls out.

to check for fuel all you need to do is remove the plug and put your finger over the cylinder while somebody turns the motor over. should have gas/oil on it

so what color spark are you getting?

one more thing, make sure the contact in the plug boot fits nice and snug. ive seen some have high resistance from people gunking them up years ago with dialectric grease

 

[who pooted?]

Is it an old Johnson Seahorse? I had the same problems with mine fowling the top plug. Points were fine, but it needed new plug wires and fuel lines. Correcting the gap was something else done. Ran fine for a while then started running rich again. I had to run the motor with the choke out for a good ways before the engine would run correct. Over time the gasket blew on the carb so I cleaned it out replaced the gasket and adjusted the slow idle. The engine would vibrate pretty bad and this caused the plate that the slow idle knob was on to vibrate which casused the slow idle knob to turn out of its set position. Now it works great! Also the motor was set up for elec. start, so got the wiring done on that too. First push start and runs great.
I've got some pics of the engine on my thread. I plan on repainting the engine after the boat is done.