Rpm change on 88 hp

[jc turtle]

Hello, my son has a 1989 88 hp Evinrude. Sometimes, the engine will jump to full throttle when you ask it to, and bring him up on plane beautifully. Other times, it will go to about 2500 rpms for a few minutes ( it varies how long )
then it will go to full throttle by itself in a second. All the coils are working
at idle on the muffs. It will also go down in rpm's at times by itself. It seems that it loses a cylinder. :facepalm: HELP!!! Where should we look for a fix? Thank you, John

 

[metriccrescentwrench]

Re: Rpm change on 88 hp

It seems that it loses a cylinder.

Well, that's probably what's happening. Unfortunately those intermittent problems are a ***** to track down. I had a similar situation with my '81 90 HP for quite awhile, most of the time it ran fine, but every once in a while would decide to act up. By the time I could do any diagnosis everything always checked out ok. Finally after one particularly bad episode I found a spark plug wire that showed infinite resistance. I was curious what had caused this so dissected the wire, someone hadn't done a good job of inserting the end into the wire. They had the edge of the connector off to the side of the wire so that it was just barely making contact.

In any case, as far as troubleshooting - one thing you can do is run your engine after dark and watch for arcing. It will also be to your advantage to have a factory service manual, there are ignition tests which are spelled out which will help you determine if a component is within specs (you'll need a digital multi-meter and a DVA adapter which you can either build or purchase for not very much). Your problem could be as simple as a bad connector between the timer base and power pack, or it could be something more sinister like a power pack going bad.

 

[boobie]

Re: Rpm change on 88 hp

Do a cyl drop test on it and see which cyl/cyls are acting up. It could be fuel or ignition probs.