Johnson outboard looses power while at speed.

[sswuscg]

I have a 2001, 70 hp, 2 stroke VRO outboard. While running 30kts for approx 20 min the engine loses power and will not push the boat more than 18 kts after this happens. The engine appears to be shaking a bit more but will stay running and re starts easily. I pulled the plugs and they were wet with oil. I replaced them and took the boat out again. Ran great... for approx 20 min. Same thing occured again.

Do I have a running rich condition or maybe trash in the bowl / high speed jets? Before it loses power there is no indication that something is not right. It does not sputter just on a dime looses power.

 

[DargelJohn]

Re: Johnson outboard looses power while at speed.

When this happens check the primer bulb. Does it go flat? If so, then you have a problem upstream of the motor: clogged tank vent, clogged pickup screen, fuel filter, fuel line, ect. To eliminate the vent, you can crack open the filler cap while running and see if that helps.

 

[jonesg]

Re: Johnson outboard looses power while at speed.

Might be overheating and dropping into SLOW, test the overheat alarm to make sure its working.

 

[idonthaveaname]

Re: Johnson outboard looses power while at speed.

I would begin by asking when was the last time it ran fine and then, what have you done since then. It could've been something simple like tighten the vent plug on the gas tank (you or someone else). Sort of sounds like venting to me...you know...runs for a while, slows, you stop the motor and the suction stops, the air seeps back in, you start the motor and it sucks the air out of the tank, slows, you stop the motor and the suction stops, the air seeps back in, and repeat. Anyhow, start the troubleshooting with the obvious and simple stuff then move on.

 

[78 mckee]

Re: Johnson outboard looses power while at speed.

I had a similar problem a while back with a 35 hp Johnson. It took a while to figure out but it turned out to be a bad stator that would intermittently fail one of the cylinders after running fine for a while. I would stop and fuss with the plugs a while and then it would run for a little while and then fail on one cylinder again. After changing plugs many times, replacing the CD power pack, rebuilding the carb, etc.; I replaced the stator and never experienced the problem again.

 

[jonesg]

Re: Johnson outboard looses power while at speed.

I had a similar problem a while back with a 35 hp Johnson. It took a while to figure out but it turned out to be a bad stator that would intermittently fail one of the cylinders after running fine for a while. I would stop and fuss with the plugs a while and then it would run for a little while and then fail on one cylinder again. After changing plugs many times, replacing the CD power pack, rebuilding the carb, etc.; I replaced the stator and never experienced the problem again.

Kindly provide the troubleshooting steps you took, or did you just guess and throw parts at it?

 

[kenmyfam]

Re: Johnson outboard looses power while at speed.

Basic health check to begin with.
Compression
Spark
Fuel delivery
Spark plug condition

Post your findings and we can all go from there. Check the "Top Secret Files" out for some good help and reading.
Any maintenance history of the motor you want to share with us ???

 

[Jayrock]

Re: Johnson outboard looses power while at speed.

First off, I am not a CERTIFIED Outboard mechanic, but I have repaired/rebuilt quite a few. Sounds like a couple cylinders are missing/not firing. The shaking is a giveaway to me. If compression is good, spark is good, and its getting plenty of fuel, try this: When the engine is first started. Run the motor like you normally would till it acts up. Then immediatley check spark, With an inductive timing light. check EACH cylinder, Should have a strong steady flash. The electronics will sometimes work normally when cool, but once warmed up, They fail. If you have a miss, I highly suggest you get a manual. No Miss, check timing. It should be fine unless something came loose or you tinkered with it. Timing good? Make sure fuel is getting to cylinders. Run engine again till problem occurs. Push in choke. Does engine speed up and perform normally? If yes, Carbs need diassembled and cleaned/rebuilt. There could be other issues, but those are the basics. Thats how I would approach the problem if I did not have a manual.

 

[78 mckee]

Re: Johnson outboard looses power while at speed.

Intermittent problems are very hard to diagnose. In my case, I did not have the diagnostic equipment to evaluate the ignition components. The problen surfaced after the components warmed-up but the interval of proper running varied wildly; sometimes days of proper operation. The first thing to do is to understand clearly the circumstances under which the probelm occures; timing, temperature, etc. Also, you need to be able to evaluate the basic things when it happens (do you have spark at each plug, etc.). I was throwing parts at it because I could not evaluate components like the CD pack and the stator was the hardest and the most expensive to evaluate and replace; it was a process of elimination. Having experienced it I might be able to shorten the process next time, but it would still be a challenge.