Troubleshooting a poor running outboard?

98 115 Johnson<br /><br />I just got back from a week vacation on Marco Island and need to look into a problem I was having all week. I realize I was taking a chance running a poor running outboard for that long but had my sons and grandchildren depending on the boat as the center piece of their vacation so I took the chance.<br /><br />Before leaving Orlando I tested the boat out in a lake and she seemed to run fine. When I got to Marco and put the boat in the water she seemed fine. I motored through the no wake zone and had no problems but after I hit open water on the way to the condo she shut down on me. She did this twice and several times the following morning. I will make this quick since I fixed that problem the next day. I replaced the powerpack and solved that problem. Since all the parts places would be closed over the Memorial day weekend I also bought one new ignition coil in case I needed it.<br /><br />For the rest of the week my motor developed a pesky little problem. She seemed to run smooth at full throttle and high RPMs but at idle speed and low RPMs she had sort of a lean cough. This was an intermit problem and happened about 50% of the time. She seldom stalled, only when she was running her absolute worst. Around mid week I decarbed the engine and cleaned the carburetors and drained the bowls and also changed out a couple of the ignition coils with the new one I had bought earlier with no change in the way she ran. <br /><br />Now that I am home I plan on doing a compression test and removing all the electronic parts and clean all the contacts and engine grounds to start. Then I will probably remove the carburetors and rebuild them. I am not sure if this is going to help but seems like a good starting point to me. Does anybody have any Ideas what might be causing the little cough the engine has at low RPMs?

Re: Troubleshooting a poor running outboard?

Just keep going in the direction your going Mike....don't forget the fuel lines. Make sure they are servicable and tight at connections.

Re: Troubleshooting a poor running outboard?

You didn't give a model number so is your motor a looper 60 degree block or the classic 90° block?<br /><br />Is the motor mounted trim switch on the port or stb. side? Port side is a 60° looper 115.<br /><br />Besides a gummed up carb, a lean spit is sometimes the result of a throttle shaft open more than the others or a linkage problem. Make sure the linkage and carb pickup timing is all adjusted exactly as described in the service manual. Check the recirculation valves also.<br /><br />Another item often overlooked is the thermostats. the motor has to run about 140°F at idle to operate properly.<br /><br />Decarbing the motor will also help free up any carbon stuck rings allowing the motor to run better, especially at low speeds.<br /><br />First do a compression check to see the condition of your motor's internal health.

Re: Troubleshooting a poor running outboard?

Before proceeding I would like to post the results of my compression test. It is in tolerance but I suspect it points to a serious problem developing. The engine is a 98 115 crossflow V4. 3 cylendars were between 118 and 122 psi. The 4th cylendar (lower left) was 110. On previous checks they were all around 120.<br /><br />I suspected a problem with this cylendar because when I pulled the plugs that plug was slightly cleaner than the others and had a little rust on it.<br /><br />I suspect somehow I am getting a little water in that cylendar but am not sure. I haven't pulled the heads yet looking for a little advice before I do.<br /><br />Oh one more note. 3 years ago I rebuilt this powerhead. I don't remember which cylendar was bad at the time but I know it was one of the lower ones. For some reason I am thinking it was the lower right but not sure.

Re: Troubleshooting a poor running outboard?

One quick update. I searched back through posts I made a couple of years ago while rebuilding this powerhead and it was the upper right that was bad back then. Not that it makes any difference but I am glad it wasnt the same one I am worried about now.

Re: Troubleshooting a poor running outboard?

I did go ahead and pull the head on the left side. I see no major scoreing in the cylendar walls. Just a couple of real light scratches. Can't even feel them with the fingernail. Can just barely feel one with the bare fingertip. I think I will pick up a head gasket tomorrow and put it back together and try another compression check. Does this sound like the logical thing to do? Oh the head of that piston is much cleaner than the top one, think I'm getting a trace of water in that cylendar? Does it sound like a head gasket or think I have a bigger problem?

Re: Troubleshooting a poor running outboard?

i'd give it a try. relatively inexpensive.

Re: Troubleshooting a poor running outboard?

Those compression numbers were OK. +/- 10% is fine.

Re: Troubleshooting a poor running outboard?

I understand that Wildone, what concerns me is the sudden drop of 10 PSI in the questionable cylendar and even more the evidence of water in that cylendar. Plus the fact that the motor isn't quite running right.

Re: Troubleshooting a poor running outboard?

Well that was the problem, thanks for the help guys. I replaced the head gasket this morning and compression on all 4 cylendars is within 2 lbs of 120. I believe the cough I was hearing is gone kind of hard to tell, those things are so damn loud out of the water but I think i got it. Thanks again.