Low RPM at WOT 115 Johnson

[mustanghorizon]

I have a 1996 Johnson 115 Ocean Runner J115SLEDR. My throttle handle was loose, so I tightened up the set screw. Ever since I have made that change, the motor will not go over 4800 RPM at WOT only hitting 34 mph. Prior to the change, the boat would hit 5500 RPM and hit 41 mph. The tightening of the throttle might be completely unrelated for all I know. There is a significant lack of power as well. I took 5 people out this past week, and the boat had a hard time getting over 10 mph at WOT, maxing out at about 4800 mph. Has anyone had a similar experience? Does the throttle linkage need to be adjusted, or does it sound like a different problem? Any help would be appreciated. I did a compression test last week, all cylinders reading 130 psi. I know the gas is good, 93 premium. Spark plugs are clean as well. Unsure what would be causing this.

 

[jakedaawg]

I wonder if when you tightened the set screw you got the handle in the wrong positiin and are now not getting wide open. Try resetting handle. Is this a flush mount remote?

 

[mustanghorizon]

I will definitely double check. If the boat still goes in forward and reverse in the same way as before, it should be correct, right? And yes, it is a flush mount on the side.

 

[jakedaawg]

I will definitely double check. If the boat still goes in forward and reverse in the same way as before, it should be correct, right? And yes, it is a flush mount on the side.

not necessarily, You could have the handle in such a place that you can hit forward but not go all the way forward. place boat in neutral. is the handle now in a vertical position?

 

[mustanghorizon]

Yes, the handle is in the vertical position at neutral.

 

[jakedaawg]

Check that the handle splines are in good condition. Check that the handle fully seats on splines.

Remove air silencer on front of carbs. With engine off advance throttle handle fully and verify that throttle plate butterflies are completely horizontal in the throat. If they are open fully perform the following:

1. Compression test

2. Open airgap spark test

3. Fuel sample into clear jar.

Report back

 

[mustanghorizon]

Ok, so the carbs are all opening pretty close to vertical. The throttle does not go all the way, but is pretty close. Compression is still 130 psi in all 4 cylinders. The gas checked out OK. I am not sure how to do an open airgap spark test though.

 

[jakedaawg]

So the throttke plates are not opening all the way? Close but not quite?

I think we should stick with the shifter handle for the moment because it ran good until you tightened the handle, correct?

Place shifter in neutral, pop of handle and reattach one spline to the clockwise or reverse if you will. Do the theottle plates now open all the way?

If so, great. If not we will need to disconnect throttle cable at linkage and check for a stretched cable. Also inspect cam follower at throttle linkage and make sure it is complete and present. Possibly post a pic of it.

 

[jakedaawg]

If you dont have a spark tester, buy or borrow one. Or try a cylinder drop test. With a pair of nylon pliers remove one plug wire at a time and listen for a change in how it runs. If removing the wire causes nothing you will need to get the spark checker.

 

[mustanghorizon]

That's right. They're not opening quite all the way. And yes, it was running perfect before the adjustment of the handle. I will adjust the handle in the morning and report back. Thank you so much for the help.

 

[jakedaawg]

emdsapmgr maybe you could help explain the handle adjustment. I think after adjusting his set screw he is no longer getting full travel and you are much better at explaining this than I. I have a hard time converting actions into words as we all know.

 

[jakedaawg]

Its either one spline forward or one spline back. Without one in front of me I have a hard time visualizing it.

 

[mustanghorizon]

Ok I will check. There is also a small amount of oil coming out of the carbs. The air silencer has alot of oil residue as well underneath the motor. It is green in color. It looks like unburnt oil. I don't know if this is normal or not.

 

[mustanghorizon]

One spline back does make more sense, because it would result in further pull of the throttle cable.

 

[mustanghorizon]

Ok. So the throttle has been adjusted so that it opens fully, but the performance is still the same. Compression is 130 psi in all cylinders. Could it be a carburetor problem? I've read through the forums that seafoaming the motor can improve the performance. Any ideas?

 

[jakedaawg]

Check max timing.

You could clean carbs paying special attention to high speed jets. Sea foam is not the most likely answer.

 

[mustanghorizon]

Jakedaawg, I contacted my local marine mechanic. He said it sounds like a fuel issue, since the prop is not damaged and the motor compression is fine. He is leaning toward a bad/clogged fuel line or water in the fuel (which I think I have ruled out). Would you tend to agree with that or does that not sound right? He said to test by running the motor off a separate gas tank with clean fuel. How would I go about this? Do I just put the fuel line directly into that 5 gallon tank and prime the bulb, or does there need to be some sort of fuel pump system? This is a huge pain in the butt.:facepalm:

 

[jakedaawg]

Borrow a portable tank and known good fuel line and bulb.

All things he said are possible. Hence the idea of cleaning the high speed jets in carbs. Sea foam will not solve anything.

Did you get any pickup in speed after getting the plates to open all the way? Higher rpms?

Is.this on an old glass boat with a soft floor in spots? Was the boat left in water or uncovered? What i am getting at is could the foam floatation under the floor now be waterlogged? Happens alot on old boats.

 

[mustanghorizon]

Yes, the boat is fiberglass. Its a 96 Four Winns horizon. The boat is trailered in and out of the water and is always covered.

There was a miniscule increase in RPM 50-75ish with the throttle fully open.

I bet you are right with the high speed jets. I will report back with portable tank.

 

[jakedaawg]

Is this a looper or a 90* crossflow? Need a model #.