Power loss on a 1985Johnson 90hp

[Salty Tricks]

Hi...I need help. I recently purchased a 1985 Whaler with a 85 Johnson 90hp. I am in the process of trying to bring this back to decent shape. The motor ran fine for several weeks of me going up and down the river. Last night after running for about 5 minutes it had a noticeble loss of power. It still was planing out but certainly less than before. Took it out tonight and same thing...ran perfect for five minutes at full speed and it loses some power. This boat also needs a new tach so giving you RPM is not possible. Any clues? Thanks

 

[OBJ]

Re: Power loss on a 1985Johnson 90hp

Welcome aboard iboats Tricks. <br /><br />Very possible your dropping a cylinder. What ya' need to do is a spark test. Make sure each spark is there for each cylinder. I got an 86' 90hp that did the same thing this past season. Found it to be the power pack to that bank of cylinders. Just one question.....does it start and run OK for a while until it's warmed up and then it starts losing rpms? The miss will be noticable coming off idle. You can feel it in the boat.

 

[Salty Tricks]

Re: Power loss on a 1985Johnson 90hp

Exactly OBJ. Runs fine for about five to ten minutes and then reduces power. Since I also just acquired a 1991 200hp evinrude for my other boat I was wondering would it pay to invest in a spark tester or can I get by with some other means of checking spark. I've been reading some other related threads and they seem to suggest that a spark gap is critical when testing. Thanks for your response.

 

[OBJ]

Re: Power loss on a 1985Johnson 90hp

A spark tester is always a good item to have on hand along with a compression tester. Here's a link to iboats store. Check them out.<br /><br /> http://www.iboats.com/mall/index.cg...age=7&current_category=tool&*******=096227010 <br /><br />If you can't find a compression tester, check with your local NAPA dealer. That's where I got mine.

 

[Solittle]

Re: Power loss on a 1985Johnson 90hp

You can also make your own spark tester. All you need is a wire to connect to each spark plug wire, a means of adjusting a gap and a way to connect each wire to ground. I made mine out of scrap "stuff" in my garage. It ain't pretty but it works.

 

[bubbakat]

Re: Power loss on a 1985Johnson 90hp

Here is a simple way to make a spark tester<br /><br /> http://nevada4.tripod.com/spark-tester.html

 

[OBJ]

Re: Power loss on a 1985Johnson 90hp

Ya' know what bubba???? I just looked at your sig line 'bout catchin' fish......I'm doin' the best I kin.......but it makes me want to P a lot..<br /><br />Speakin' of spark testers.....a cut off nail will work to. 16 penny. Just stick it in the end of a spark plug boot, hold it with insulated pliers about 1/2" away from a clean engine ground and have someone crank the engine. Cheap....but effective.

 

[Phil Miller]

Re: Power loss on a 1985Johnson 90hp

What would cause the loss of a cylinder? It is always the power pac? Is there a way to check the power pac?

 

[fireman57]

Re: Power loss on a 1985Johnson 90hp

Switch the wires from one pack to the other cylinders and see if the problem follows it. No spark, replace that pack. Powerpack not always the problem. Could be stator, loose or burned wire, bad ground, gremlins, etc..... Just that the pack is easy to check and is the culprit a lot of times.