1983 115 Johnson, need help

[barnacle]

Hello,

About a month ago the motor started acting up, it starts right up and idles pretty good, every once in awhile a little cough, but not bad.

When driving at slow speeds it cuts out on one cylinder, when I open it up it coughs a few times, then seems to run on all of them. when I slow down, it runs OK for a bit, then starts cutting out again.

I pulled the plugs and all looked good except the upper starboard one which was black, but not oily. I put new plugs in and it did the same thing.

I checked the compression, 110 on all cylinders.

I checked the spark with a spark gap tool set at 5/16th inch and they all seemed to have a good spark at cranking speed with the plugs out.

Next I pulled the carbs and took them apart, they were clean, no water or dirt, I blew out all the passages anyway and put it back together, still the same problem.

Then I swapped the powerpacks from one side to the other, still the same plug would be black, but not oily.

I put a new coil on that cylinder, still the same.

I pulled the top carb again and looked at it real good and still could not see anything wrong.

I don't know what to check next, any help would be appreciated, thank you.

 

[darrklim2]

Re: 1983 115 Johnson, need help

Could you try to swap the carbs around. I don't know much about this engine so I don't know how many carbs you have but I would suspect the "black" plug would follow the carb. To me it sounds like that cylinder is getting too much fuel at low speed and therefore fowling it out causing the black color to the plug. Just my thoughts.

 

[darrklim2]

Re: 1983 115 Johnson, need help

Also, from what I understand that engine should be able to jump a 7/16 gap with a bright blue spark for each cylinder. I know thats not much more than the 5/16 you said but maybe that will be it.

 

[barnacle]

Re: 1983 115 Johnson, need help

Thanks for the quick reply.

I thought about doing that, and I still might try that, but I hate to mess up the linkage adjustments.

The thing that gets me is that the plug is black with carbon but bone dry.

 

[barnacle]

Re: 1983 115 Johnson, need help

I'm back,

Swapped carbs today, little tricky because I did not want to remove throttle plates so cut an old parts carb for another throttle lever. Anyway the problem stayed on the same cylinder. At least now I'm sure the problem is in the ignition.

By the way, I forgot to mention that I had already run it in the dark to look for sparks jumping.

Any ideas what I could try next?

Thanks.

 

[barnacle]

Re: 1983 115 Johnson, need help

back again,

This is getting stranger the the more tests I make.

What I did tonight is run the engine with #1 plug wire hooked to the spark gap tester, with the plug still in the engine. The tester was grounded and I got a good blue spark at 1/2 inch gap, even when reved up.

I then did the same to the other three, same good spark.

Now I'm not so sure it is in the ignition.

Talked to a friend who sugested that the problem might be the mixture in that cylinder, maybe caused by a bad top crankshaft seal or the reed valve. I don't know how the crankcase is designed or if this possible.

I'm running out of things to check, don't know what to do next.