Please Help 120hp Johnson

[amoore51]

I just bought my first fishing boat today its a 1992 Skeeter SS140 Fish and Ski with a 1992 model 120 horsepower Johnson. I took it out on the lake for some fishing and all was well!! I was cruising aroung the lake at about 40-50 mph on and off for about 2 hours. When I got ready to head back to the dock I took off and came up to a bridge so I slowed down to a speed just above idle. When I opened up the throttle to take off again the boat wouldnt go faster than about 15 mph. I slowed down turned the boat off and restarted the motor, put it in gear and gave it full throttle again, only 15 mph max speed. I turned it off again and did the same thing and it took off back to normal. Once i got back the the boat dock I slowed it back down to a trolling speed and when I went to load the boat same thing wouldnt go but about 15 mph. Can someone please give me some advice I dont know anything about boats, what could cause this what should I do???

 

[jjacobs007]

Re: Please Help 120hp Johnson

check all gas lines and oil areas.also check electrical wires for shorts are loose wires or grounds.

 

[jonesg]

Re: Please Help 120hp Johnson

new to you I would go through it top to bottom.
if you don't know the condition,

compression test, seafoam treat it.

rebuild the carbs,
There are videos on youtube showing how to do this, very simple.

change the lower gear oil,use new seals on drain screws!
change fuel filter,
remove prop and clean prop shaft,
regrease shaft, look for fishing line on shaft ( it will destroy shaft seals)
replace sparkplugs (save old ones for spares)

spark GAP test it per the manual (obviously get the factory service book).

Thats a great engine but its real easy to melt a piston if you just go out and run it without knowing everything is up to date. All it takes is a bit of dirt in a carb to burn a piston.

It might sound like overkill but the techs will tell you its almost impossible to wear these outboards out, they always fail due to lack of upkeep.
Don't go out until it runs right, except for brief tests.

 

[shipwreck]

Re: Please Help 120hp Johnson

check over heating to , t-stat and good pee stream .
I had t-stat good bad and took from 25mph- to 5mph miles hours

 

[AEROCOOK]

Re: Please Help 120hp Johnson

See if the carbs are opening up all the way when you push the throttle lever all the way forward. (not while its running)

 

[amoore51]

Re: Please Help 120hp Johnson

Thanks guys for your input I really appreciate that. Where are the carbs located and how do you get to them? Also how do you do seafoam tratment and what does that do? Also I noticed that when I pulled the boat out of the water the water that was "peeing" from the motor was really hot is that normal?

 

[ezeke]

Re: Please Help 120hp Johnson

Yor motor has the S.L.O.W feature that automatically reduces RPM to 2800 when the engine overheats. You should troubleshoot your cooling system before anything else.

S.L.O.W resets itself if the engine is turned off AND the engine temperature is back to normal.