1974 johnson 115 cylinder problem

[norman2013]

Hey guys, I have a 1974 johnson 115 on my four winns fish/ski boat and it isn't running right. I took the boat out last week and it seemed to run good, the motor go up to speed an ran decent but last night I went to take it out and it ran terrible. It wouldn't get up to speed and it kept sputtering. For a few seconds it would run good but then it would start acting up. I did a compression test and all cylinders have good compression. I also checked the spark and all plugs jumped a large gap. Then i did a cylinder drop test and it appears that the bottom left cylinder is not working? Any suggestions?

 

[Bosunsmate]

Re: 1974 johnson 115 cylinder problem

Ground the plug wire out and then turn it over a few times, check that plug is getting wet with fuel

 

[norman2013]

Re: 1974 johnson 115 cylinder problem

I just inspected the plug and the gap has some how closed on it. Like somthing as bent it down?

 

[Bosunsmate]

Re: 1974 johnson 115 cylinder problem

i actually had that on my lawnmower yesterday.
Time for a new plug, dont just bend it back as it may snap off soon

 

[norman2013]

Re: 1974 johnson 115 cylinder problem

What do you think would cause it to bend down while it was screwed in?

 

[Bosunsmate]

Re: 1974 johnson 115 cylinder problem

fatigue
if you move that cyl to top dead centre see if you get much play by pressing on the piston head with something through the sparkplug hole (nothing sharp) dont scratch the piston.
you a checking the bearings for that piston doing that.
I doubt they have gone since your compression is ok and if they were gone enough to hit the sparkplug you would be hearing a definite knocking

 

[emdsapmgr]

Re: 1974 johnson 115 cylinder problem

If the j part of the plug is bent, something hit it. Possible a ring let go. Recheck your compression and compare that non-firing cyl compression with the others. If it's low that's not good news. Shine a pencil light into the spark plug hole and look for any piston crown damage. You may need to pull the head on that side for a better visual inspection.