Logo
FULL SITE MENU

2000 Johnson 50hp Model J50PLSSM

Jupiter Dinghy

Jupiter Dinghy

Regular Contributor
I have recently acquired a runabout powered by this motor, and was wondering if the rough idle/slow speed run was the nature of the beast (it's a 2 cylinder / big bore) or if I should look into some settings to smoothen things out on the low end?
Mid range and full throttle runs are a charm, runs very smooth and delivers plenty of power, but when hitting a slow or idle zone, the motor shakes the whole boat with vibrations.
Idle in neutral is fine also (smokes a bit then but it's 2 stroke so nothing shocking there I guess)

Any feedback from anyone with experience with those twin cylinders 50hp motors welcome. Thanks!
 
I have the same motor and it idles smooth, Have you checked the timing? spark? once in a while when first starting at the boat dock, if its been a few weeks not run, mine is a bit stubborn to get running smooth and smokes quite a bit for a few minutes until its warmed up, I also set the idle and the carb mixtures in the water in gear, and varify the timing and idle speed is correct. The mixture I check by slapping into wot (no bogging, flat-spotting)for a few seconds and quickly chop the throttle to see how the motor acts...no popping, dying out.
 
joeanna said:
I have the same motor and it idles smooth, Have you checked the timing? spark? once in a while when first starting at the boat dock, if its been a few weeks not run, mine is a bit stubborn to get running smooth and smokes quite a bit for a few minutes until its warmed up, I also set the idle and the carb mixtures in the water in gear, and varify the timing and idle speed is correct. The mixture I check by slapping into wot (no bogging, flat-spotting)for a few seconds and quickly chop the throttle to see how the motor acts...no popping, dying out.
Click to expand...

Thanks for the feedback joeanna, and yes the smoking on initial start up after a week or two of rest seems to be characteristic, as mine does it too (kind of a lot).
I was afraid 110 compression was on the low side for this motor, do you know what your is?
Will check timing (guess I need the manual....) and go from there
 
Just checked my compression and timing on my motor, 95 on both warm, timing was 1 degree ATDC. I just had to verify I had the correct numbers :)
 
joeanna said:
Just checked my compression and timing on my motor, 95 on both warm, timing was 1 degree ATDC. I just had to verify I had the correct numbers :)
Click to expand...
Thanks for the follow up and the info! (I feel better about my compression numbers now) :)
I don't have a timing light yet (or a manual), is the timing checked at wot? Any required RPM?
 
OK, so I got me a timing light and tested it on the motor (never used one of those before so forgive my ignorance). It works great but I'm either not using it right, or my timing is way off.

1st question: If I'm looking for 1 degree ATDC (after top dead center), am I looking for the red mark or the green one on the pic below? (I'm thinking the red one but wanna make sure)

ih16s8.jpg


2nd question: On the timing light there is a timing advance knob, the manual says "set it on the Zero mark", so what is the purpose of that timing advance knob?... to find out by how much the timing is off by turning it until the desired mark faces the index?
 
Last edited:
Red mark. I glued my knob at zero, its use is to set the timing light for the advance you want and will strobe the zero indicator when that advance is meet, some flywheels don't have decent or any high degree marks.
 
joeanna said:
Red mark. I glued my knob at zero, its use is to set the timing light for the advance you want and will strobe the zero indicator when that advance is meet, some flywheels don't have decent or any high degree marks.
Click to expand...
Ah ok..... I tried turning this knob while strobing the flywheel at idle until the 2 marks aligned (for my 1 degree ATDC), and when they did align, the button on the light was on the 10 degree mark, so I was wondering if that meant my timing was off by 10 degrees ...

I finally found the factory service manual at a decent price online should get it early next week and will work on the timing then. Are there several adjustment rods to play with for the advance setting?
 
Facts-----Maximum timing advance is set at the factory for the life of the motor.--------Idle timing has to do with where throttle OPENS UP.-------Actual idle timing looks after itself and is set with idle speed stop screw for proper idle RPM.------Do not adjust things that you are not 100% sure of.
 
racerone said:
Facts-----Maximum timing advance is set at the factory for the life of the motor.--------Idle timing has to do with where throttle OPENS UP.-------Actual idle timing looks after itself and is set with idle speed stop screw for proper idle RPM.------Do not adjust things that you are not 100% sure of.
Click to expand...

I see, thanks Racer. And Joe actually told me that in a separate inquiry, mentioning the idle timing was automatically taken care of by the wot timing advance.
I will get a tach on it and check the idle RPM.

So when you say "Maximum timing advance is set at the factory for the life of the motor", it means that timing will never go off or cannot be affected ever, as long as the flywheel remains on the crankshaft correct?
 
Correct-----The only way timing changes is if the flywheel key shears.-------And no , you can not find a sheared key with your timing light either !!
 
Back
Top