1999 Johnson 50 inconsistently running poorly

16ftstriper

Cadet
Joined
Jul 10, 2020
Messages
6
I recently got a new boat with a 1999 Johnson 50 2 cylinder 2 stroke. The first time I took it out it ran decently, but started to bog at WOT towards the end of the trip.

To attempt to remedy this, I did new spark plugs, installed a water separating fuel filter, new fuel filter, topped the tank with 93, put seafoam in the tank, sprayed seafoam upper engine spray through the carbs while running, and removed the VRO pump and switched to premix (disconnected oil hose and capped off the nipple, disconnected the 4 wires from the pump and the 2 from the tank).

When I took it out today to test it, it was not running well at all under load. It would not go past 3K RPMs and was extremely slow. It revved well in neutral, just not in gear. It was also consistent in the issue, and didn't fluctuate power levels. I tried to turn it off and back on again, and had a really hard time starting (usually it fires up immediately). I took it home and looked everything over and it started right up and ran great. I brought it back to the water and this time it ran better than ever, really fast and no bogging. My brother accidentally pulled the kill switch lanyard, so it died while driving. When I went to start it back up, it had a hard time starting like it did before, and after about 60 seconds it did the same thing as before, no power under load and wouldn't rev past 3K. It idled fine and didn't die both times that it was acting up.

I'm leaning towards some sort of electrical issue because it was running poorly, then great, then poorly again after being turned off and on a bunch of times. If anyone has an ideas or suggestions I'd like to hear them!
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,881
The trouble shooting starts with a compression test.-----Then a spark test.-----Maybe check flywheel key.----Test run with another tank and hose ( borrow one ) , some plastic tanks are poor quality.
 

16ftstriper

Cadet
Joined
Jul 10, 2020
Messages
6
Compression is around 120PSI in both cylinders. I agree that a spark test should probably be the next thing to check. What would I check on the flywheel key? I’m pretty new to outboard ignition systems.
 

16ftstriper

Cadet
Joined
Jul 10, 2020
Messages
6
I plan on checking the flywheel key, spark plugs and wires, and cleaning the carbs as soon as I can. That seems to be the first logical step. The strange thing about the way it is acting is how it is inconsistent. Right before it acted up for the second time it was running better than it ever was. Would the flywheel key being sheared lead to the timing being off all of the time, or just sometimes?

Here's a short video I took of it while it was acting up: https://youtu.be/XF-rKj-hnsU
 
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