70s Johnson 15- Fuel/Choke Problem?

[tysonnathan]

I have what I believe to be a late 70s 15hp Johnson Seahorse. The motor was given to me by a friend when he replaced it with a four stroke. It can be a little difficult to start at times even when it is warm. When I first got it I ran it in a barrel for a while and it got the water a lot greasier/nasty than my other small outboards do. I took it out and it ran pretty well after I got it cranked. It was running pretty strong but the priming bulb felt soft every time I grabbed it. When I squeezed it the motor would speed up a little. While running around @WOT, I reached down and pulled out the choke, just to see what it would do. When I did, the motor caught another gear! (so to speak).. It sounded like it was only running at 1/2 or 3/4 throttle before that. After that the bulb still seemed to lose prime. This is an older motor with a good many hours on it, but I would really like to use it as my #1 engine as it is nearly twice the hp of my most dependable engine (8hp Mariner). Anyone have any ideas?

 

[brandon.prewitt]

Re: 70s Johnson 15- Fuel/Choke Problem?

I'm new here, but it sounds to me like all you need to do is clean the carbs, bro.

 

[brandon.prewitt]

Re: 70s Johnson 15- Fuel/Choke Problem?

You could have a problem with the check valve at your tank, too.

 

[tashasdaddy]

Re: 70s Johnson 15- Fuel/Choke Problem?

i'm in 100% agreement with a good carb cleaning, and a rebuild kit. we need to know the model # on transom bracket, to determine year and correct parts. also check for any leaks in fuel lines. vent open on the fuel tank.

 

[tysonnathan]

Re: 70s Johnson 15- Fuel/Choke Problem?

The tank is vented and the fuel line seems to be fine.... Sprayed in carb cleaner but havent taken it off. Is it hard to rebuild one? I have done it on a Briggs b/f but not an outboard. What about the oil residue in the barrel after running it?

 

[tysonnathan]

Re: 70s Johnson 15- Fuel/Choke Problem?

Also, sorry I dont have the model numbers... Im on the road traveling right now.

 

[tysonnathan]

Re: 70s Johnson 15- Fuel/Choke Problem?

Ok... So it has been a while since I first posted this thread, but I just got around to working on this motor again. I put a carb kit on, replaced the entire fuel pump assembly, and replaced fuel lines. Also found the top ignition coil to be bad and replaced it. I think that the misfiring was causing the gunk and oil in the barrel I was running it in... After all of this work the motor still wouldnt crank well w/o the assistance of starting fluid, but once cranked it would run pretty well. So I took it out to try it on the water and it wouldnt crank at all (even w/ starting fluid). So I took the carb back off and checked it for trash. Blew it out and put it back on. It will crank some of the time now but it is hard to keep it running. I have to have the choke set to just the right spot or it will shut off. I checked the plugs and it seems that after I clean them they foul up really quickly (esp. on the top cylinder). I pulled the head off and the cylinders look decent. The top one does seem to hiss and bubble a little more when I turn the flywheel though. I checked compression and they are both around 100, but I dont know how fast they leak down. Does anyone have any ideas as to what might be wrong? Any help would be greatly appreciated!

BTW... Its a 1975 year model.

Thanks,
Tn

 

[timsmcm]

Re: 70s Johnson 15- Fuel/Choke Problem?

I would say that you might have a stopped up venturi in the carb. and also does the spark at the plugs look good and strong may have some weak spark going on.

 

[tysonnathan]

Re: 70s Johnson 15- Fuel/Choke Problem?

What is a venturi? The spark is blue and looks to be fairly strong. It did shock me once though and it didnt seem to hurt as bad as I remember it being from other trucks and motors...

Tn

 

[tysonnathan]

Re: 70s Johnson 15- Fuel/Choke Problem?

Why can't I get any help on this???

 

[Rick.]

Re: 70s Johnson 15- Fuel/Choke Problem?

This is my third time writing this reply. I keep hitting the wrong button and my post gets lost. Anyway here goes.

I still am not convinced your carb. is clean. Tear it apart completely and soak it overnight. Then clean it with spray carb. cleaner and make suer you get every orifice and channel from all directions and then blow it out with compressed air and carefully put it back together. Please remember your not looking for the kind of dirt that falls out when you tap the carb. on the side of you bench vice. The dirt could be in the form of gum deposit or tiny pieces of crud that are restricting the flow of gas. Your low speed needle valve must be correctly set and the packing for that needle valve should be replaced as well. Your fuel pump isn't the likely cause of this trouble but you made a good decision to replace it because of the age of the motor. Your compression readings are fantastic and should be a positive influence on getting this motor running right. You will trash the compression if you continue to use starting fluid to accomplish ignition. Mix some gas/oil in a spray bottle and use that for priming if required. The gas primer bulb should be soft once the motor is running. At that point it is under suction from the fuel pump. When you choke the carb. you are mostly making the air/fuel mix richer. Lastly I must encouage you to get a factory OMC service manual. You will find it so very useful and it has great detailed information about how to set up your motor and do many many repairs yourself. You must realize that this forum is a great assistance to all of us with outboards. However it is a lot of typing and thinking to respond to posters. If you have a more in depth understanding it takes less typing to reply, like asking an educated question. There is a vast amount of knowledge represented on the forum and you will get the help you need but make sure you listen to the advice given and then respond with the results. Check out the links below.
Best of luck, Rick.

http://forums.iboats.com/forumdisplay.php?f=31
http://forums.iboats.com/showthread.php?t=167352
http://www.sschapterpsa.com/ramblings/OMC/OMC info.htm

 

[tysonnathan]

Re: 70s Johnson 15- Fuel/Choke Problem?

thanks for the relpy Rick. I cleaned the carb again with no change. I finally got it running by taking the flywheel off and filing and readjusting the points. I ran good for a while and then the motor started to skip on one cylinder. When I got done the plugs looked clean. I think a point might be fouled up again or the ignition coil that I didnt replace might be skipping. Is there anything in the ignition system that fails when the motor gets warm? Again, I really appreciate your response! I will discontinue starting it with starting fluid. Thanks for that bit of advice.

Nt

 

[tx1961whaler]

Re: 70s Johnson 15- Fuel/Choke Problem?

The coils, points, and condensers probably need replacing. If you do all that at once, you won't have to look under that flywheel again for another 15 years....

 

[jbjennings]

Re: 70s Johnson 15- Fuel/Choke Problem?

The coils, points, and condensers probably need replacing. If you do all that at once, you won't have to look under that flywheel again for another 15 years....

I totally agree, especially if you keep having intermittent spark. When your motor heats up, the tiny coils of wire in the coil may have a tiny break which opens up when the heat causes it to expand.
I also totally agree with your advise on getting that carb spotless. Does it "cough" or "sneeze" on idle? If so, either your carb. is dirty or your slow speed adjustment needle is misadjusted, or you have a vacuum leak. Good luck and don't worry, you'll get it right!
JMO,
JBJ

 

[tysonnathan]

Re: 70s Johnson 15- Fuel/Choke Problem?

Thanks guys. I think that the carb is clean, as it is not showing any of the signs you describe. Its just an obvious skip at slow idle. If I idle it down too low without fluttering the throttle it will die. I think I will replace the other ignition coil and the points and condensors. The motor was given to me so I can afford to invest a little more in it... Thanks for the help. I will post back when I get the new parts on...

Tn

 

[tysonnathan]

Re: 70s Johnson 15- Fuel/Choke Problem?

So, I installed the new ignition coil and a new points set today and the motor is still skipping. I have replaced points and condensors, both ignition coils, fuel pump, and rebuilt the carb. The motor does run better but is still skipping at low rpms. If I slow the boat down to an idle and then accelerate enough to get the front of the boat out of the air but not to plane it out it kind of stutters and skips for a little while. After a few seconds the other cylinder will start firing and it will take off. If I give it all of the throttle it will usually take off w/o a noticable skip. Does anyone know of anything else that may be causing the problem? I feel like the only thing left in the ignition system that has not been replaced is the stator(I think thats what its called... the magnet under the flywheel that produces electricity) and the wires that run to and from all of the ignition componets. Any thoughts??


Thanks
Tn

 

[Rick.]

Re: 70s Johnson 15- Fuel/Choke Problem?

Sorry but I'm not sure what to suggest next. The only thing I could suggest is to make sure to clean the magnets on your flywheel. I'm not sure how to trouble shoot the stator. Rick.

 

[tysonnathan]

Re: 70s Johnson 15- Fuel/Choke Problem?

Thanks Rick...
Anyone else got any ideas?

Tn

 

[Rick.]

Re: 70s Johnson 15- Fuel/Choke Problem?

This is troubling. I purchased a cheap little inline spark tester for my mower many years ago. One end goes on the plug and the other on the plug wire. When you have spark it lights each time the power goes through it.(which is a lot) Funny thing is I never ever used it on my mower but it has proven to be very handy working on these outboards. Perhaps you could see if you can find one at your local auto parts store. It takes less than a minute to move from one plug to the other. The nice thing is you put it inline and run the motor so you get an accurate real time picture of what's happening. With it installed you should be able to see which plug isn't getting any spark when it acts up. From there you can start testing your new parts if you have a meter or for that matter you could swap them out (one part at a time) to the other side and see which part is giving you trouble. This device doesn't tell you if you've got strong/weak spark, but it will tell you if you have spark. To test for strong spark you need a device that has an adjustable gap for the spark to jump across. Your comment about it taking off when you give it full throttle (and other symptoms you mention) indicates the spark is not your issue but that your carb. is not working right. Anyway, sorry to throw you that curve ball. Continue to work on the spark issue until you can eliminate it as a factor. When you get beyond this problem you will like your motor even more. You mentioned when you filed the points it ran good for a while. According to your post you also cleaned the carb. at the same time. Have you changed the fuel line from the pump to the carb.? Maybe it is breaking down and sending fragments of rubber to the carb. Don't give up. Rick.

 

[tysonnathan]

Re: 70s Johnson 15- Fuel/Choke Problem?

Rick,
Thanks again for the response. I am almost positive its electrical. When it runs it cuts in and out. Runs like a top for a second, then skips and shakes for a second. The problem being so sporatic leads me to believe that it is not the carb. It runs just like my old Sears motor does when the points get fouled up. I will try to get one of those lights you are talking about and see what the spark is doing when it acts up. I'm thinking that I may have a wire with the insulation worn off somewhere... Possibly where the wires go through the timing advance/retard plate below the flywheel??? That part moves with the throttle and a wire could be rubbing in there... I dont know... I am away from home until this weekend so it will be a while before I can tinker with it.

Tn