1979 Johnson 15 HP runs erratically - I fixed it!

Hi guys,
I'm looking for some advice.
I own a few older Johnson outboards and have been doing some basic maintenance on them. I don't have much experience with motor repair and have basically been doing some greasing and other minor repairs on them.

I am having some issues with a 1979 15 HP motor I own. It is a model 15R79E and it sat around for a year after I had a starting mechanism failure. I fixed the issue (spring) and just recently put it back in use.

The problem I am having is that when it runs it won't stay a high speed for a long duration of time without sputtering to a slow (almost idle) speed. If I bring it back to idle it stays running but then has issues getting back up to high speed.

After reading some of the forums I troubleshot to fuel delivery issues. I have replaced the entire hose (new hose, pump bulb and clips) to no avail.

My question is: Would you think I have a fuel pump issue or a carburetor issue?

It does run at a trolling speed for hours ( I just went fishing all afternoon) and will run at high speed continuously sometimes without issues. It just won't go at top speed without doing the sputtering thing and going through a hesitation interval.

Any help would be appreciated as I am hesitant to just go out and buy a new fuel pump or carburetor rebuild kit.
Thanks

Re: 1979 Johnson 15 HP runs erratically

Re: 1979 Johnson 15 HP runs erratically

I would personally remove, clean, and rekit the carb. Make sure to remove the plugs and clean behind them. Examine the venturi tubes for hair line cracks. Venturi tubes are not replaceable. If they are cracked you would need a new carb. Here is a link to carb kits for your motor here at iboats. http://www.iboats.com/mall/partfind...gd_poid=355609&gd_row=26&**********=117145324

Re: 1979 Johnson 15 HP runs erratically

Re: 1979 Johnson 15 HP runs erratically

Cofe,
A carb rebuild is certainly a cheaper start than the fuel pump replacement. I don't think the carb has ever been rebuilt and I've owned this engine since 1993 without doing so.
I notice that the part link you provide is for a kit without a replacement float. Shouldn't I replace the float too?
What's the difference between the Mallory and Sierra kits, If any?
Thanks

Re: 1979 Johnson 15 HP runs erratically

Re: 1979 Johnson 15 HP runs erratically

In addition to doing the above, check that all connections are tight with no air leaks and the tank and motor connection o-rings are not leaking air. Make sure tank vent is wide open and check the filter screen on the end of the pick-up tube in the tank is not clogged. Good luck.

Re: 1979 Johnson 15 HP runs erratically

Re: 1979 Johnson 15 HP runs erratically

Will Bark said:

In addition to doing the above, check that all connections are tight with no air leaks and the tank and motor connection o-rings are not leaking air. Make sure tank vent is wide open and check the filter screen on the end of the pick-up tube in the tank is not clogged. Good luck.

Click to expand...

I replaced the hose/tank connectors already. The tank in an old school OMC tank with no vent other than the cap which is either on or loose, I've never had issues with the tank and I have a '72 6HP that has run without issues using the same tank and hose setups. Will check the pick up tube though. I was actually planning on buying a new gasket for the tank when I buy the carb kit.

Re: 1979 Johnson 15 HP runs erratically

Re: 1979 Johnson 15 HP runs erratically

I haven't had much luck with Sierra kits. I would choose the Mallory. You won't need a new float.

Re: 1979 Johnson 15 HP runs erratically

Re: 1979 Johnson 15 HP runs erratically

Parts are on their way for a Carb and Fuel pump rebuild.
I also bought new gaskets for my fuel tanks so I can clean them out too.
Will post after I get all this done to give results.

Re: 1979 Johnson 15 HP runs erratically

Re: 1979 Johnson 15 HP runs erratically

Parts (Carb kit and Fuel pump kit) came in on Wednesday and today I worked on the motor.
The motor had a roughed up starter spindle so I had ordered one of those too. I replaced that first as you need to remove the starter recoil mechanism to get to the cab nuts.
I took the Carb off and inspected it, it was very dirty.
Once I took off the fuel bowl I realized I had made a great decision in ordering the kit with the replacement float as the original cork and lacquer float was still present and quite deteriorated.
There was a lot of noticeable residue on the orifices so I cleaned them up.
I cleaned the bowl and sprayed a lot of carb cleaner on the entire carb.
I took out the slow speed needle and the old gasket fell apart in the process, It was totally shot.
I sprayed carb cleaner and blew air through all orifices and then started to replace the parts with the new ones from the kit.
Put everything back together without issue and had a cigar.

Then I tackled the fuel pump rebuild. This was a lot easier than I thought it would be and in no time I had it all cleaned and rebuilt.

I took the motor out of the basement, put it on my stand and filled up a garbage can with water.
After attaching the fuel hose I primed the bulb and pulled the choke. It started on the second pull.
The thing was purring and seemed to be running fine. I didn't need to make any adjustments to the slow speed knob at all.
Next I put it in gear and it ran just fine.
I put it back on my boat and grabbed my tools just in case and went for a spin.
The motor ran great, flying and high speed and puttering along at trolling speed.
I made a slight adjustment towards the rich side for the slow speed adjustment and the thing didn't stall once.

It's running better than it ever has in my possession, I've owned it for 18 years.
I might add that I have never done anything like this repair in my life!
Thanks for all your help!

Re: 1979 Johnson 15 HP runs erratically

Re: 1979 Johnson 15 HP runs erratically

Cofe said:

I haven't had much luck with Sierra kits. I would choose the Mallory. You won't need a new float.

Click to expand...

FYI:
I did in fact need the new float as the old one was still present and was made of old cork and lacquer.
Glad I ordered the kit with the float or I'd be stuck waiting for a new float!

Re: 1979 Johnson 15 HP runs erratically - I fixed it!

Glad you got it fixed! I thought for sure that the old cork float would have been replaced long ago.......wrong...... Thanks for posting back, now get out there and fish

Just a thought..... A water pump should be replaced every 5 years max........If yours hasn't been replaced, it would sure need it before it breaks. A overheat in a outboard causes lots of problems, and it is simple to do . If you decide to replace it make a new post and we will help you out.

Re: 1979 Johnson 15 HP runs erratically - I fixed it!

Hmmmm. Water pump eh?
I seriously doubt that has been replaced..... Maybe over the winter months.
As noted before in the other post, I put the motor back on the boat to really test it out. I do have another of these old Johnsons, It's a 1971 6 HP Model 6R-71E. Maybe I'll do all this stuff to that one and then redo the water pump on the 1979 15HP. Is the water pump a rebuild project or strictly a replacement item. I was really surpised how easy it was to rebuild the fuel pump.

Re: 1979 Johnson 15 HP runs erratically - I fixed it!

The water pump is repairable and totally replaceable. It is best to disassemble the water pump to find out just what you need before ordering. Usually the pump housing is ok, and all you will need is a water pump kit. A copper water tube runs from the water pump to the power head and has a rubber grommet on each end. Those would need to be replaced also. The impeller in the water pump is made of rubber, and rubber degrades and cracks over time. That is the reasoning for fixing water pumps before they fall apart and the motor overheats. BTW Great job on fixing your carb and fuel pump for the first time. Water pumps are easy too. You may become a seasoned mechanic yet....

Re: 1979 Johnson 15 HP runs erratically - I fixed it!

Thanks for the info.
Sounds like a job best tackled in the off season due to the ordering of the parts after taking it apart.
I'll be in touch...

Re: 1979 Johnson 15 HP runs erratically - I fixed it!

+1: Listen to Cofe... Just order the whole kit. ~$36 iboats sierra 18-3327 with housing and everything you need or boatsdotnet omc $38.#0389112

When people do the job piecemeal (I've done plenty) they usually omit the replacement of the driveshaft to housing seal and never develop proper pressure/volume.

Get the kit and you'll have no surprises and have - as new - water pressure/volume.

Use the wide water tube grommet that comes in the kit (vs the small grommet). It'll be obvious when you've got it apart. Makes it easier to re-connect the water tube.

You've got a good running highly sought after motor. I can do the job in 30minutes, you'll take 2hrs tops. 7 bolts the lower unit is off(6 plus shifter). 4 bolts on water pump.

There are TONS of guys on this forum that know that motor every which way from Sunday, so you'll breeze through it.

Now, get your order in!

Re: 1979 Johnson 15 HP runs erratically - I fixed it!

While your at it. Find a factory manual on Ebay - normally about 20bucks.

Re: 1979 Johnson 15 HP runs erratically - I fixed it!

yes.this seal is important.i put regular automotiv seal.
the preasure is strong.
also i put this bigger gromet/in kit you recive 3 type of gromets/
drill 2 extra holes in midsection botom to drain water from midesection and no water left over in mid section