Logo
FULL SITE MENU

1985 Johnson 15 horsepower

R

RJ61

New member
I have a Johnson 15 horsepower outboard it runs great but doesn't rev up very high or go very fast. The videos I see with this motor goes about 24 mph and I'm not anywhere near that
 
Welcome. First off, did it EVER run faster? What size and model boat do you have? If a longshaft motor is mounted on a short shaft boat it will rob performances as well. Low compression may be another issue as well as the incorrect propeller, which would not allow the motor to rev up to its specified RPM. We would love to have the model number too because sometimes people change the motor cowling and the 9.9 will fit on the 15 and vice versa.
 
Running on 1 cylinder.-----Check compression post the numbers here.----Does spark jump a gap of 3/8" on a test device? ,
 
racerone said:
Running on 1 cylinder.-----Check compression post the numbers here.----Does spark jump a gap of 3/8" on a test device? ,
Click to expand...
I don't have a compression tester. I can get one and check it. It seems to run smooth but wide throttle doesn't wind up the engine much
 
Sorry----You have to do the work.----I cannot get my hands on your motor from 1053 miles away.-----Does throttle open fully?----Any pieces just above the carburetor broken ?----Answering questions can help us lead you to the problem !
 
racerone said:
Sorry----You have to do the work.----I cannot get my hands on your motor from 1053 miles away.-----Does throttle open fully?----Any pieces just above the carburetor broken ?----Answering questions can help us lead you to the problem !
Click to expand...
No there's nothing broken on the carb. I had the carb fuel pump and water pump replaced. The throttle opens fully
 
timguy said:
Welcome. First off, did it EVER run faster? What size and model boat do you have? If a longshaft motor is mounted on a short shaft boat it will rob performances as well. Low compression may be another issue as well as the incorrect propeller, which would not allow the motor to rev up to its specified RPM. We would love to have the model number too because sometimes people change the motor cowling and the 9.9 will fit on the 15 and vice versa.
Click to expand...
Yes it ran faster before it was adjusted. It's definitely a 15 horsepower the DNR guy who inspected it told me it's a 15 with a 9.9 cover. The propeller is chipped up. The number on it is 8172x10 when you open the throttle wide open it doesn't wind up the engine very much
 
timguy said:
Welcome. First off, did it EVER run faster? What size and model boat do you have? If a longshaft motor is mounted on a short shaft boat it will rob performances as well. Low compression may be another issue as well as the incorrect propeller, which would not allow the motor to rev up to its specified RPM. We would love to have the model number too because sometimes people change the motor cowling and the 9.9 will fit on the 15 and vice versa.
Click to expand...
The model number is CJI5ECOB Canada
 
Some will argue.----I think it is running on 1 cylinder.----Easy to figure out with simple test.-----Start motor.----Pull wire off top sparkplug.----Repeat and pull bottom off.
 
Does it idle smoothly? It will not idle smoothly on one cylinder firing only. Did someone with good qualities do the carb work? Did it start acting up after a storage period....say 6 months or longer?
 
racerone said:
Some will argue.----I think it is running on 1 cylinder.----Easy to figure out with simple test.-----Start motor.----Pull wire off top sparkplug.----Repeat and pull bottom off.
Click to expand...
Ok thanks
timguy said:
Does it idle smoothly? It will not idle smoothly on one cylinder firing only. Did someone with good qualities do the carb work? Did it start acting up after a storage period....say 6 months or longer?
Click to expand...
Thank you to everyone for the help. Yes it idles smoothly . It was a good mechanic who did the carb work. The mechanic who did the work wasn't a boat engine mechanic but a excellent mechanic on small engine and any gas or diesel engine. That's why I had a guy from a marina adjust it after the first guy. But before I took it to the marina guy I had it out on the river and it went faster but was erratic so I had him adjust it. I ran sea foam in it and it will idle down all the way now. It runs good it just won't wind out or go very fast at all and I wondered if that could be an adjustment in the carb or something
 
Okay, Racer is right. We can start with a spark jump test. Pull out the spark plugs and then put a #2 Phillips screwdriver in the spark plug boot. Have the fuel line disconnected for safety. Have a helper pull over the motor.
 
Sorry had to help my wife with something, the post writing time expired.
Carefully hold shank of screwdriver 3/8" from the ground object, like a coil mounting screw. Check for nice strong lightning like blue spark. Keep your hand on the screwdriver handle or you might get a good jolt, don't touch the steel screwdriver shank. The reason we remove the fuel line is to eliminate the source of a highly combustible substance....
 
You can post pictures here but you must size them under 1000k, then we can observe the condition of the motor and wiring, etc. If the paint is discolored on the cylinder head or mice have attacked it....you get the idea. There really are no common adjustments that will effect high speed, so looks like we are dealing with a failure of some kind, and not an adjustment here.
 
racerone said:
Why not do some simple trouble shooting----See post #3 on this.-------Your location ?
Click to expand...
timguy said:
You can post pictures here but you must size them under 1000k, then we can observe the condition of the motor and wiring, etc. If the paint is discolored on the cylinder head or mice have attacked it....you get the idea. There really are no common adjustments that will effect high speed, so looks like we are dealing with a failure of some kind, and not an adjustment here.
Click to expand...
Ok thank you I will
 
racerone said:
Why not do some simple trouble shooting----See post #3 on this.-------Your location ?
Click to expand...
My location is southern Ohio. I just got a new prop and shaft seal kit yesterday. There was a small amount of oil when I removed the old prop that was chipped and pretty beat up.im going to change the plugs as well and see if that helps but it runs and idles smoothly
 
racerone said:
They run very well on 1 cylinder.----Just no power to move a boat.
Click to expand...
I'll try the
timguy said:
Sorry had to help my wife with something, the post writing time expired.
Carefully hold shank of screwdriver 3/8" from the ground object, like a coil mounting screw. Check for nice strong lightning like blue spark. Keep your hand on the screwdriver handle or you might get a good jolt, don't touch the steel screwdriver shank. The reason we remove the fuel line is to eliminate the source of a highly combustible substance....
Click to expand...
Ok thanks I'll try that and report back
 
Back
Top