1988 Johnson 25hp Outboard bogging down under load

[Tmac908]

I have a Johnson 25hp outboard. Model # j25rcca. The outboard was working great when it began bogging down whenever I put any load above idle on the motor. It would bog down and if I didnt back off on the throttle the motor would die. I realized that pulling the choke helped the issue so I completely cleaned and rebuilt the carb but the problem persisted. I went out and bought a new oem primer bulb and that did not help either. I have also replaced the spark plugs.

Last time I had it out on the water I discovered that if I continued to pump the primer bulb while giving throttle, the engine would hesitate for a few seconds then perform perfectly. Once I went through this process it would continue working perfectly (no additional bulb pumping needed) until I shut the motor off. If I started the motor again I would have to repeat these steps to get it working.

Could this be a fuel pump issue? I know that normally when pumping the bulb manually helps, it is an issue with the fuel pump, I just found it strange that manual pumping was only needed for a few seconds initially to get everything up and running then was no longer necessary. I do not want to keep spending on rebuild kits and fixing the wrong part like I did on the carb.

 

[Bosunsmate]

Might be a sticking fuel valve/float in that carb.
Perhaps, also, some air leaks in to your fuel line while its sitting

 

[Tmac908]

I have tried a few different fuel lines and even tried a new tank and that didnt help. When i had the carb apart the the float seemed to move freely. I do not think there was an issue with that as far as i could tell.

 

[Bosunsmate]

im out of ideas, exorcisms arent my thing.
But i always check the fuel float is working properly by turning it upside down and trying to blow in the fuel intake. It shouldnt take any air and then turning it right way up and checking it will accept air straight away

 

[Tmac908]

I will give that a try, thanks for the help

 

[Tmac908]

That did not do the trick, I am pretty convinced that the carb is not the issue. Anyone else out there have any advise for me?

 

[racerone]

The high speed jet that screws in the very bottom of the float bowl is clean ?----Throttle plate opening too early perhaps ?----What does a compression test show ?

 

[oldboat1]

Think I would replace the pump diaphragm, based on the symptoms you describe: http://ww2.iboats.com/Fuel-Pump/dm/cart_id.584977335--session_id.887635542--view_id.1537647

 

[Tmac908]

The high speed jet is what i thought the issue was originally. I made sure it was pristine before i put the carb back together. I will check out the throttle plate and if that does not work I will go ahead with the pump rebuild. Thanks for the advise I will post the results

 

[oldboat1]

should check compression, though, as suggested above. Need to know if the motor has more serious issues before proceeding (borrow a tester if you don't have one -- auto parts stores are often a source.)

 

[Saintnowhere]

could be fuel pump, fuel tank not venting properly or the fuel hose connectors o-ring might be leaking.

 

[Tmac908]

Today i got the fuel pump rebuild kit and rebuilt the pump. The old diaphragm did not appear to have any hole or be in bad condition. I also took a compression test and got 90 on both cylinders. I plan on taking to boat to the river the first chance i get to put it under load and see how it does.

While i was removing the plugs for the compression test I noticed that the plugs (which are new and only have about two engine hours on them) seemed to have a dark deposit on them. Il attach a pic of both plugs. Im obviously no expert on motors, does this look bad?

 

[Vandkanten]

I have a 1987, 25 HP. And I had the same problem.
Replace fuel with fresh fuel with correct oil 1:100, too much oil = oily plugs (nr. 2 not oily spark looks good, but try fasten the plug abit more, you should nor have oil or anything else on the upper part of the plug, see photo)

Replaced plugs. Replaced fuel pump (dont buy china)
Air blown all fuel lines, one by one. Check fuel line from tank. And arrow on pump pointing at engine?
Clean carb. use very small needle to clean the small fuel holes. Use a powerfull flashlight and see if you can see the light through the small holes, else clean again.

 

[racerone]

Service bulletin came out to say that these motors run on 50:1 and remove 100:1 stickers, as 100:1 was not correct for them !----Compression of 90 PSI is low.----Check with another gauge.----Checked the water pump lately ?

 

[Tmac908]

I do run on 50:1. And I also think that the compression reading may be low because of the gauge. the one i have never seems to show high readings and I have used it on multiple engines. I will check with another gauge but this motor has been reading 90 with my gauge sine the day i got it and was performing great before this issue started.

Vandkanten I have tried all of the things that you mentioned besides air blowing the lines. I have now tried on 3 different fuel lines 2 cheap ones and one OMC line. I have also tried on 2 different fuel tanks. If the pump didnt work im thinking that replacing all the internal lines and fuel hose connector might be my last thing to try.

 

[Tmac908]

Oh and racerone I did replace the water impeller about a month ago and replace the seals/gaskets in the water pump. Seems to be working good. Could that be contributing to the issue?

 

[BTL]

I have this same motor, and mine developed a crack in the small primer line leading to the carb that was causing some issues until I replaced it.

 

[Tmac908]

Thanks BTL. I guess changing the lines will be my next step. Was the crack in the primer line on your motor visibly leaking fuel?

 

[oldboat1]

Plug is likely Champion QL77JC4 with a couple of other options. Gap would typically be .030. Torque value 18-21 ft lbs (216-240 in. lbs).

 

[Tmac908]

I took it out to the river tonight. The problem is as bad if not worse. Now the motor will barley idle. The only time I could keep the motor running was was when the choke was pulled out.

I disconnected the fuel line that ran from the pump to the carburetor after I filled the carburetor bowl using the bulb and it was pumping a good amount of fuel when I ran the motor. I guess the last thing I can try now is to replace the fuel lines that are under the cowl.

If that does not work i guess i am off to the mechanic. I dont want to have to take it in but i cant think of anything else to do.