90 HP Johnson- Erratic operation

[LakeMonster]

I have a 1982 90 HP Johnson that is acting very strange. I can have the boat out on the lake and it's running fine (defined as pushing 30 to 32 mph max) at WOT. All of a sudden, like a switch, the boat speed drops and begins to max out at 15 mph and I feel like I'm crawling across the lake (sounds like the engine is still at top RPM while this is happening which is weird). On another occasion, I'd be cruising at no wake speed with the engine seemingly running fine and all of a sudden the engine seems to run more stable (less shaky) and with some additional power. It seems, at these "stable" times, that the engine will hit the higher MPH if I were to punch the throttle. I can't link this to any temperature or amount of time out on the lake in one outing. It just comes and goes. I noticed some burn marks on the engine head by coil #1 so I replaced all the coils and plug wires (what's with the plug wires? They have a little hook that presses through the enter of the plug wire in the hopes that you can contact the core of the wire and keep consistent connection through the visbration of the engine on the lake) Anyway, after I replaced the coils and wires the problem still exists. I can be out all day and not have the problem occur or I can go out and have the problem there the entire time. Any advice would be greatly appreciated.

 

[scrampbell]

Re: 90 HP Johnson- Erratic operation

Sounds like clogged jets in your carbs. To clean them out (you have two on each carb), take out the plug screws and *gently* poke the end of a paperclip in there to dislodge any gunk. This should get you going. Let us know how it goes.

 

[LakeMonster]

Re: 90 HP Johnson- Erratic operation

Thanks scrampbell, I'll give it a try.

 

[emdsapmgr]

Re: 90 HP Johnson- Erratic operation

It's possible that an ignition component is failing at times, causing a loss in power. It's easy to test for spark with an inductive timing light. Check the spark on all 4 plugwires when the engine starts to act up. (best if the engine is under load, like idling in gear.) The 4 coils and 2 power packs on that engine are all identical and can be swapped for testing purposes.

 

[LakeMonster]

Re: 90 HP Johnson- Erratic operation

I was also told it could be a bad stator. I'm really new at this. Is this a possibility? If so, how to I check the stator's preformance?

 

[LakeMonster]

Re: 90 HP Johnson- Erratic operation

OK, update- so I had the engine idling when the problem occured this weekend. I got out the timing light and found that their was spark on every cylinder but #1. I swapped coils and plug wires with cylinder #3 and the problem stayed on cylinder #1. Should I be looking for a new power pack or could there be another problem?

 

[scrampbell]

Re: 90 HP Johnson- Erratic operation

Sounds like the power pack is a leading candidate. As emdsapmgr hinted at, you can verify by switching the two power packs and retest. You don't have to fully install the power packs when you switch them, just make sure the ground(s) are grounded and connect all the connectors. The pack will just kinda hang there.

If problem follows the power pack then replace the pack. If problem doesn't follow the pack then you need to move further upstream and test the stator and/or timer base.

 

[Pokertrampp]

Re: 90 HP Johnson- Erratic operation

sounds like the engine is still at top RPM while this is happening which is weird.

By this statement, it sounds like you are spinning the prop.

 

[captncrunch]

Re: 90 HP Johnson- Erratic operation

I had a similar problem with my 89 88spl. Evinrude. Turned out it was a small crack in the wires running from the coil pack. I wound up taking my to the local mechanic after I cleaned the carbs, replaced the plugs and wires and still it was an intermittent problem. The wires on mine are brown and cracked/arched where they make the turn from the stern side of the motor starboard side of the motor.

Hope that helps.

 

[LakeMonster]

Re: 90 HP Johnson- Erratic operation

I just took the boat to a repair shop to have it diagnosed. They said that the stator was supposed to put out 150 volts - it was putting out 40 to 100 volts. Should I look at replacing the stator and, if so, how tough is that to do on my own?