Johnson 60 sluggish and stuttering at WOT

[Kruegs35]

I'm hoping someone here has some ideas, because I am all out. I have a 1992 Johnson 60 on a 16' Hydra-Sports center console. I cannot get on plane and my top speed is between 10 - 15 mph depending on the conditions. At WOT the engine starts stuttering and no more speed is gained. The engine idles great and seems to run at low speeds just fine. The primer bulb gets hard and full of fuel.

Here is what I have done so far:

Replaced the fuel/water separator - I did not see any water in the fuel
Replaced the fuel filter
Rebuilt the carbs
Replaced the fuel pump


Here is a video of the engine, it is not great, but maybe it will help. At about 4 seconds, I go to WOT.

 

[emdsapmgr]

Check all 3 spark plugs for spark. It may only be running on 2 cyls. I'd also do a compression check on all three cylinders.

 

[Bosunsmate]

look at you sparkplugs too, one may be a different colour than the others

 

[Kruegs35]

All cylinders are between 105 - 110. All spark plugs look similar and have good spark.

 

[WernerF]

Looks like SLOW mode or erratic igition. Have you a tach mounted?

 

[Kruegs35]

No, i dont have a tach

 

[WernerF]

SLOW mode is the rev limiter (inside the powerpack) at about 2,500 rpm triggered by the overtemp switch. But the warning tone should go off when the overtemp switch closes.
Does the horn sound when you turn the key to RUN position? Does it sound continuously when you ground the overtemp switch lead (tan or tan/blue)?

 

[Kruegs35]

I get a single beep everytime I turn the key. I'll have to test grounding the wire tomorrow.

 

[emdsapmgr]

While this comment has relevance, it may not be the only problem with your WOT operation. But here goes: Looks like the engine may be mounted too low on the transom. When on plane, the water flowing from under the transom is hitting he lower unit ABOVE the antiventilation plate. When setup this way, and the water flows above that plate, you will get poor performance due to excess drag. Also, excess water spray from that plate "dragging" in the water. This will also result in lousy fuel economy. The water flowing from under the transom should run just under the antiventilation plate.

 

[Kruegs35]

WernerF - is this the wire you are referring to? I grounded it and did not get any noise.


Emdsapmgr-thanks, I'll take a look at the mounting height.

 

[interalian]

Ground the motor end, not the pigtail from the sensor.

 

[Faztbullet]

Index the flywheel and then check timing on each cylinder...had a 1996 60 act the same way and it was a bad flywheel(hub magnet)

 

[Kruegs35]

So, I get a single beep when I turn the key to the run position and a continuous beep when I ground the wire to the sensor. Does this mean that my warning signal is working, thus ruling out SLOW mode?

 

[WernerF]

Yes, it rules out SLOW mode for external reasons (overtemp switch or wiring). But there is the pssibility left that the powerpack falsely enters SLOW mode.

You still don't know for sure whether to fight a fuel or ignition issue.

You may hook up a timing light on all cylinders and look for irregular flashes when the engine starts stuttering. I myself prefer "listening" to the ignition with a headphone and an old AM transistor receiver wrapped in a plastic bag and placed near the engine, because it can be done alone on the water.

 

[Kruegs35]

I've never checked timing before and I don't have an old AM receiver. I appreciate all of the responses. I think it is time to go to a mechanic. I have spent too much time trying to fix it myself and save some money, and my family is getting frustrated that we cannot enjoy the boat. I'll be sure to post the results.

 

[Kruegs35]

I haven't taken the boat to the mechanic yet. I was working replacing the impeller first because I wasnt getting good flow from the pee hole anymore. Anyway, I am still not getting good water flow when i increase the rpms and i wasnt sure if this could have any relation to the lack of power. When I'm at idle or low rpms, the water from the pee hole is very strong. After I ramp up the motor, the flow slows and eventually dies. I can turn off the motor for a bit and some flow comes back. Is this something with the thermostat? Could this be causing SLOW mode?

 

[Bosunsmate]

sounds like a leak into the water jacket somewhere which is pressursing the cooling system with gases and thus heating it up and maybe putting it into slow mode.
When it stops peeing is air blowing out of the telltale?

 

[Kruegs35]

I'll have to check the air. What would cause that? Head gasket?

 

[Bosunsmate]

I'll have to check the air. What would cause that? Head gasket?

headgasket, exhaust gasket, base plate gasket etc

 

[Kruegs35]

Engine is peeing just find now, not sure why, but it seemed to work itself out. I tried to take the boat to the mechanic today, but he said it would be 3 weeks before he could touch it. He did recommend to push in the choke while at WOT to see if the rpms surged.

I have read something about using suppressive style spark plugs, like the Champion Q plugs, instead of the resistive type plugs, which I am running now. Is that worth trying for my situation?