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J90tlcte

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Fire

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Hello all I was wondering how to inspect the pistons on a 90 hp outboard. I believe there are some type of inspection covers somewhere that are easily accessible? And the gaskets are fairly in expensive. Any help would be awesome.
Thanks
 
You can see the sides of the pistons by removing the intake and exhaust covers. The intake covers are two on each side of the V-engine block. The exhaust cover is the pregnant-looking thing inn the back, between the V.

Why are you looking? It's not something you would do unless there is some sort of a problem.
 
Thank you, the boat stalls when going from forward to reverse, I had done a compression test which shows 110 to 125 psi per cylinder, someone told me to check for piston scuffing. I am new to outboard motors. I am an automotive mechanic so I do understand the principles but this is also a very old motor? Not sure what to do next ran seafoam in gas last season also
Thanks again
 
Take a look at the throttle lever on the motor. Observe how the motion is limited at idle speed by a screw with a spring around it. That is your idle speed screw. Screw it in to increase idle speed, out to reduce idle speed. You should do this with the throttle cable disconnected and move the lever with your fingers. Then adjust the cable to fit the motor, never adjust the motor to fit the cable. NOTE: Not to be confused with the screw that limits full throttle movement. Keep your hands off that unless you know what you are doing.

Just offhand, I don't know the correct idle RPM. Likely around 650 with motor warmed up, in forward gear, on the boat, on the lake.
 
Hello again now the that the weather warmed up a little I did take a look at the motor but do not see a screw with a spring on it? Am I missing something?
Thanks
 
Hello again, I do not have the screw with the spring in the linkage like the picture.What I do have is a threaded rod that is L shaped that is attached to the linkage is that what I have to adjust? I tried to attach a picture but could not get it to work. Thanks again for your help
 
110-125PSI compression is a bit bigger difference than you really want, but it's not the end of the world. Do you happen to have 125 top and bottom on one side and 110 on the other side? If so, I seem to recall some engines had a compression discrepancy between port and starboard but I forget which ones.

By chance are you going straight from forward to reverse during this shift, or are you first stopping at neutral then shifting to reverse? I'll defer to our more seasoned veterans on this one but I wonder if there is a safety switch that prevents direct shifting from F to R so you don't munch the clutch dog and/or gears?

What is your idle RPM in gear, in the water with a warm engine? If it's around 650 then you're probably okay on idle speed. Next time, try to first stop the shift lever in neutral, pause, then go to reverse. If the problem persists then it's not a safety switch.

KJ
 
I stop in neutral and first then as soon as it's shifted to reverse it stalls making docking very difficult. Thank you
 
Motor that stall need trouble shooting to find the cause.-----Best to remove those bypass covers to inspect pistons and rings !!----The parts book shows a " throttle stop screw "on this motor.------Missing parts always makes me wonder as to the maintenance this motor has been subjected to if any !!
 
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Fire said:
Hello again, I do not have the screw with the spring in the linkage like the picture.What I do have is a threaded rod that is L shaped that is attached to the linkage is that what I have to adjust? I tried to attach a picture but could not get it to work. Thanks again for your help
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No!! Do not "adjust" the threaded link! That will mess up the synchronization. Perhaps your picture is too big. Try reducing the size of it.

Also, no there is no shift interrupter switch.
 
Trying to figure out what in blazes you have. Missing parts? Not really a 90TLCT? Anyhow, here is how it was done on some older motors, but I doubt you have this either or you would have seen it by now. Waiting for picture.
 

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Fire said:
I don't have that idle screw and it's definently a J90TLCTE I will try to upload a photo again thanks
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Go to the engine diagrams on this site, For your motor, under cylinder & crankcase, the idle screw will be part # 75. But...

If you haven't cleaned your carbs, it's probably time to do so. A small speck of something can easily bock an idle jet. When you are cleaning them, run a single strand of copper wire through the jets. You can find their location in the engine diagrams.

I have a 1990 Johnson 90 hp that wanted to die at idle, especially when shifting. After cleaning the carbs, I also ran a can of Johnson Engine Tuner through my motor. It's simple. Follow the instructions on the can. You might have surprisingly good results. I did.

MY motor idles higher than I have seen from others on here. In the water, in forward gear, my motor idles at 800 rpm. It shifts perfectly, and never dies at idle.

Good luck, and don't give up. With then help from these smart fellows, you can get her right!
 
Ok guys I cannot get a picture of this to upload on this site is there something special that needs to be done??? I did check out the diagram but all I see on my linkage is that rod that I Believe syncs the carbs and another screw with a rubber plug on the end that looks like it acts as a stop thanks
 
Do not adjust the screw with the " rubber plug " ------I can not believe that the idle stop screw is missing on this motor.------Hurry to a shop / friend / neighbor and have this pointed out to you.
 
Here is your picture. I don't know why you couldn't find the idle screw. Maybe because the spring is behind, out of view. Anyhow, it arleady is screwed in further than normal. I suspect there is something else wrong with the motor, not developing normal, equal power at idle. Full troubleshooting is required if you can't bring the idle speed up some more.
 

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Trouble shooting needs to be done.----See post that encourage you to remove the bypass covers.-----I believe there is something wrong with pistons / rings.-----Cost you some time and new gaskets to find out.
 
So I was finally able to get the boat in the water and adjust the idle slightly which seemed to make it better shifting from forward to reverse!! I can't thank you enough for the help. I do have one question regarding the shifter when the boat is put in gear the high idle lever guys up on it's own and won't stay down Any tricks to that??
Thanks John
 
Fire said:
So I was finally able to get the boat in the water and adjust the idle slightly which seemed to make it better shifting from forward to reverse!! I can't thank you enough for the help. I do have one question regarding the shifter when the boat is put in gear the high idle lever guys up on it's own and won't stay down Any tricks to that??
Thanks John
Click to expand...

I would assume that problem popped up due to too much tension being put on the idle stop screw.

The proper method to adjusting the idle is to back off the idle adjusting screw so that it is not touching it's stop, then adjust the adjustable threaded trunion on the throttle cable to set the idle THEN adjust the idle adjustment stop screw so that the idle cannot drop under your preferred setting.

You'll need to loosen (or remove) the clamp plate that retains the throttle cable trunions in order to turn/adjust them.
 
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