Johnson 15hp

[moser42]

Johnson 15hp motor, On the ID tag it says:

serial # - C 8489003
model # - CJ15RESR
Outboard Marine Corporation
Canada

Could someone please tell me what year this motor is? the owner told me it was a 1991 or 1990.

It has always been in fresh water, what is the best way to clean off algae(yellow color) on the lower end of the motor? any household cleaners that might help?

I sprayed seafoam deep creep into each cylinder and black oil came out the drain holes on the lower end which means its cleaning her out.

What are the proper spark plugs for this motor?
Does this motor have a thermostat and where is it located?

Thanks alot for your help!

 

[HighTrim]

Re: Johnson 15hp

It is a 1990. For plugs use QL77JC4 gapped to .030.

 

[1730V]

Re: Johnson 15hp

At minimum, you need to do this:

1. Change the water pump impeller.

2. Service the lower unit. Get new drain/fill plug seals-cheap.

3. Decarb it. See the "decarb" article in FAQ's for outbords.

If you do this stuff, it will run forever.

 

[Rick.]

Re: Johnson 15hp

I would guess you have a good motor here but the first thing I would do to it is check the compression. If that is good do all the stuff listed above. Hope it turns out great for you. I have an 82 15 hp and it runs fantastic. I also have a 90 9.9 yahtwin that I will probably go over this winter. I hope it checks out good on the compression test as well. Rick.

 

[moser42]

Re: Johnson 15hp

compression was good, about 120 on each cylinder. starts and runs fine, lots of water coming out the tell tale. Should I be checking the thermostat?
Need some grease and some cleaning up but started first pull.
The motor revs up fine in gear but when I switch to neutral it will only idle, when I turn the throttle in neutral the motor just idles. Can i get a high idle in neutral or just in gear?

Thankss alot!

 

[1730V]

Re: Johnson 15hp

Moser,

There is a mechanism that stops you from over revving in nuetral. It only lets you get about 1/2. That's a good thing. You do not want to be spreading internal engine parts all over the place.

120 psi in both lungs is good. It's healthy. If you want to make it healthier, go the FAQ's section and look up "Decarbing your engine".

If you have good water flow, as described, that's good. I would still replace the water pump impeller as insurance.

Service the lower unit with new drain and fill plug seals and you're good to go.

That engine will run forever with a bit of care.

 

[Cornell]

Re: Johnson 15hp

No one has answered your question about thermostat. It is located on upper part of the engine and is a triangle housing if it is the same as my '88 15hp Evinrude which I believe it is. My motor doesn't warm up and I have plans to replace the stat. The motor can't be as efficient when the motor doesn't get up to operating temp. Feel the water exiting the water pump hole and see if it warms up after a few minutes. I'm sure that the carbon will form again soon if it doesn't get up to proper temp.
By the way, someone helped me with the de-carbon process with Seafoam and it really cleaned things out and helped a lot. I don't want to get back into that same problem so I will surely change the stat.
Iboats has them I think or someone on line. Seemed to be around $20?? But it didn't show a housing gasket included. You might want to get that as well. If you can't find it check with Napa auto parts as they have a marine manual. Someone with more Outboard experience may be able to shed more advice here.


Cornell

 

[moser42]

Re: Johnson 15hp

1730V-- "There is a mechanism that stops you from over revving in nuetral. It only lets you get about 1/2."

My problem is that the rpms do not change at all when i turn the throttle in neutral, It will only idle in neutral and I have to put it in gear to rev it up so it won't stall after idling a while. I know it should let me rev it to about 1/2 but i can't get anything higher then low idle in neutral.

Cornell - thanks for the help! lots of water out the tell tale but it was cold the whole time I ran it(15-20 minutes) idling because I couldnt rev it up in neutral on the muffs. Is water supposed to exit out the exhaust above water, on the back of the motor? or does all the water exit through the tell tale? The block did not seem to heat up.

Thankss!!

 

[HighTrim]

Re: Johnson 15hp

Most of the spent cooling water will exit via the tell tale. You should not rev your motor high on muffs, not as big a deal on a smaller motor, but keep the rpms down on the muffs, mainly for troubleshooting. I would also reccomend getting yourself a manual for this motor, it will pay for itself a million times over.