Semi-random loss of power

[svdk]

1981, 115hp Evinrude<br /><br />First time out this season we had no problems. Second time out this season we decided to pull the kids and wife in the tube. <br /><br />1st problem- Engine ran well with everyone in the boat (no tube). When I began pulling folks in the tube the engine ran normal for 15 to 30 second then lost power just as we would get up to plane. It seemed that the engine was just bogging down. During moments of low power the engine would experience intermittent surges. I would run the engine at low rpms for 5 to 10 minutes and the try to accelerate only to repeat the same problem. We ended up just pulling the tube around at a trolling speed (very low rpms), pulled the tube in at the end of the day and the motor seemed to operate fine.<br /><br />2nd problem- I left everyone off at the dock and took the boat for a quick spin with a full tank of gas. The boat got to plane easily, ran at full throttle for about 30 to 40 seconds, then experienced complete loss of power with no noise or warning. The engine re-started fine and I decided to load up the boat.<br /><br />I'm guessing, these two issues are related. Correct? <br /><br />I plan on checking a few things tomorrow, but was wondering if anyone can help narrow down my search for the problem.<br /><br />Fresh gas was used during the whole trip. Engine never got hot. Carbs were rebuilt and cleaned last season. Gas tank and fuel lines were replaced last season. No similar problems from motor last season. <br /><br />Any ideas?<br /><br />Thanks in advance,<br />Stephen

 

[jbndt]

Re: Semi-random loss of power

I had a similar problem with a 96 Johnson 112. I took it to the shop and they told me I needed the carb rebbuilt, I protested, since it ran perfect when it was cold, but they were the experts. Well, got it back, ran for a while then started the same thing. Mine would be running full speed then just quit. It would then fire right back up?! I ended up running it until it started acting up, then calling the mechanic to come to the boat $$$. It ended up that the power-pack was breaking down when it got hot. Had it replaced and it ran fine. Good luck.

 

[svdk]

Re: Semi-random loss of power

Thanks jbndt. I'll keep that in mind as I trouble shoot this week.<br /><br />I plan on checking compresson and spark first. I'm assuming if that checks out okay and the plugs look okay, I'm probably dealing with an intermitent electrical issue when the motor heats up. Is this a correct assumption?<br /><br />I not too fimilar with outboards. If the power pack is breaking down, will the motor still be capable of output? What harm will occur if I continue to use the motor with a bad power-pack, other that being stranded?

 

[jbndt]

Re: Semi-random loss of power

1st - I am not a mechanic. I don't see how the boat would "run fine for 30-40 seconds" if the compresion were bad. In my situation, when the engin got hot (after running under load for a while) the spark was affected causing it to miss or shut down. It would usually fire right back up and run fine for a short time. I wouldn't try to run that way unless you have oars with you ;-)

 

[hamburgerman]

Re: Semi-random loss of power

Sounds like you are losing a cylinder check the coils they get hot and act up

 

[svdk]

Re: Semi-random loss of power

When the weekend gets here and compression and spark pans out ok, how do I go about checking the coils, power-pack, or stator for intermitent failure.<br /><br />Thanks,<br />Stephen

 

[fireman57]

Re: Semi-random loss of power

Take a timing light and a buddy and check each spark plug lead when it does this.

 

[Captain Jeff]

Re: Semi-random loss of power

Did you figure out the problem?

 

[svdk]

Re: Semi-random loss of power

fishonceo,<br /><br />The weekend was busy with yard work, church and father's day stuff. Hopefully, I'll get a chance to look at this week.<br /><br />Thanks,<br />Stephen

 

[svdk]

Re: Semi-random loss of power

Checked compression and spark this morning. Compression was good: 125, 125, 130, 125 (top left, bottom left, top right, bottom right). Spark was strong on all four (tested at 7/16th in)

All plugs looked similar with top right being the driest, but all slightly wet. Insulators were all tan and dry.

I don't see any fuel restrictions.

I guess I need to take it out on the lake for some testing under load. Any other ideas--Coils, power pack, ??

Thanks,
Stephen

 

[hoolapool]

Re: Semi-random loss of power

.....having a similiar problem here with a Johnson 70.:%

Run and idles great..then suddenly dies and subsequently restarts.

powerpack? is it an easy replace?

Best,

Mack

 

[svdk]

Re: Semi-random loss of power

Well its been awhile, but I've found a little time to work more on this issue.

I think I found the fuel restriction that may be causing the problem. I decided to clean/rebuild the carbs since I have two kits left over from last year's rebuild.

In the seat for the needle valve in the lower carb I found a small sliver of rubber--looks like a very small piece of fuel line. I think the rubber was choking the flow as the motor picked up load.

Am I correct? Could this cause the drop in power under load? I'm hoping that was the problem.

Well I have a few more things to check out. Hopefully that solves the issue.

Hoolapool,

Did you ever solve your issue? I haven't dealt with the power pack replacement as I hope this carb rebuild will fix the problem. I still want to check the fuel pump and a couple more fuel related issues before diving into the electrical issues.

SVDK

 

[jdupree]

Re: Semi-random loss of power

svdk,

I would zero in on the power pack. I have a 1988 90hp Johnson that was displaying the very same symptoms when under load. I pulled and re-built my carbs with no joy. Power pack was replaced and runs like a new one.

John

 

[svdk]

Re: Semi-random loss of power

Well, the carbs will be going back on today. Hopefully we'll see if that fixed the problem. That piece of rubber I pulled out, while small, was big enough to cause problems with the needle seating properly. I really hope that was the only problem.

I may need to look at the powerpack next. It may be a few more weeks before I can get out on the lake to take a test run. In the meantime, I plan to plan to lync and sync.

In looking in the manual, it says to first set the timing pointer first. I don't have a "piston stop" to use in setting the timing pointer. It ran good before this problem, does the "timing pointer" need to be reset after just removing/replacing the carbs?