Best Spark Plug to Use and what type

[dpostman21]

I have a 1965 18 HP Johnson. I see some pages showing the J4C, J6C and others showing J8C spark plugs. I have been using the J4C and it runs ok just the plugs look pretty "wet" / "Black" Bottom one almost looked fowled out (going to recheck points gap) but ran ok just didn't seem to get top end RPM. never stalled and started fine.

See Pic https://goo.gl/photos/MsywhjDKUARUDa1L9

 

[flyingscott]

You may have a cylinder not working do you have spark on both.

 

[dpostman21]

Yes. Spark and good compression. So to be far these were new plugs when I replace coils and points but did not have them gapped correctly in the beginning so they could be funky from that.

Have used at least 8 tanks of gas through it since the points replacement

 

[Vic.S]

I have a 1965 18 HP Johnson. I see some pages showing the J4C, J6C and others showing J8C spark plugs. I have been using the J4C and it runs ok just the plugs look pretty "wet" / "Black" Bottom one almost looked fowled out (going to recheck points gap) but ran ok just didn't seem to get top end RPM. never stalled and started fine.

See Pic https://goo.gl/photos/MsywhjDKUARUDa1L9

J4C are the recommended plugs.

Only consider J6C if you have fouling problems.

I cannot see J8C listed for any Johnson or Evinrude

 

[dpostman21]

Thanks Vic.S makes sense just a little hotter plug I assume. the J8C would likely burn a hole in the cylinder. I will recheck gap on points and throw fresh plugs in it tonight and see.

 

[HighTrim]

I myself run J6C in mine. None need the J8cs. I find the J6C a good plug for both trolling and wide open throttle.

 

[dpostman21]

Chris - Thanks for the information.

I recent changed lower unit on my 18 HP 1965 Johnson, I looked at the file for rod adjustment but not sure how to measure. I have a simplex with type 400 cables (new) and I can not get forward gear tried adjusting cable but just don't get there. I can manually move it in all gears just not with controller. Guessing I need to adjust rod height. Before the lower was swapped I had no issues getting all gears.

I have started another thread but thought I would run it by you.

 

[hardwater fisherman]

I dont think shift rod height is adjustable on that motor.

 

[dpostman21]

thanks I was wondering how because it has the "ball: at the end of the rod that's locked in by screw.

 

[hardwater fisherman]

Try adjusting the controls to the motor. And not the motor to the controls. If you know what I am saying.

 

[HighTrim]

Agree with above, never adjust the motor to suit the controls, always adjust the controls to suit the motor. If the motor shifts manually fine, there is something wrong with the controls, or the cables, likely shot.