1990 Johnson 15HP wont stay running (long story)

[Moustache]

Hey everyone! I'm new here but have been lurking for the past 2 weeks trying to get my old Johnson running with no luck.

A little history - I purchased a 12' aluminum boat 2 weeks ago and it came with a trailer and a motor. The johnson i am having trouble with. It felt like a good deal being able to pick up a boat, trailer and engine with titles for under $500. I was told that the engine sat for 2 years in a shed before i purchased it. Before sitting, the engine was supposedly tuned up and running great. I figured a good carb cleaning would do the trick. I have built and worked on quite a few automotive engines so i figured this would be a piece of cake.

First thing on the list was to clean the carb and replace the plugs. So i pulled the carb and cleaned all of the parts. The gaskets looked good so i reused them and changed the plugs. Built a wooden engine stand and set up a tub of water for the lower end to sit in. I could get the engine running and keep it running in neutral and in gear. Everything seemed to be working, water out of the little hole, spinning the prop both directions without any problems. So i mounted to the boat and set off with the girlfriend the next morning. Unfortunately, by the time the boat was in the water, the engine would not stay running. We ended up spend 3 hours on the dock next to the ramp, tinkering away trying not to drop anything in the bay. Thank the stars for the world most patient girlfriend!

So after the first failed attempt i took the boat home and put the engine back on the stand. Pulled the fuel pump to find a large amount of black, dirt-ish looking particles behind the filter screen. There is a local marina which stocks, what seems like, every johnson part available. so i called them and picked up a fuel pump rebuild kit, carb rebuild kit, a manual and a waterpump kit. Went home, replaced all of the fuel lines and fittings from the tank to the carb and rebuilt both the fuel pump and carb after a thorough cleaning. Reinstalled everything at the same settings they were at before and now cannot keep it running longer than a few seconds. Choke in or out. Very frustrating.

I have checked the compression which looked fine with the top cylinder @ 118 and the bottom @ 110. Tested for spark, and tested the fuel pump to ensure it is in fact pumping. the primer ball stays relatively firm while it runs. Pumping it when it bogs, does not make a difference. I'm begining to lean towards an ignition problem since it is the only system that has not been touched yet. I wanted to seek the advice of you all before throwing any more parts at this thing. Any and all suggestions would be greatly appreciated.

Great forum by the way! There is an incredible amount of information on here!

Here's a video of about how long this little guy will actually run.
https://www.youtube.com/watch?v=FFA6ypM0BEQ&feature=youtu.be

 

[schematic]

check the top plastic carb body for cracks

 

[schematic]

check the top plastic carb body for cracks

 

[Moustache]

The top plastic was cracked and was replaced with the rebuild kit. New needle and all. forgot to mention that in the original post. I've tried it with the needle turned all the way in and then 1 1/2 turns out. and have tried it at 2 1/2 turns out which is what the OMC directions called for that came with the new top plastic kit i bought. Thanks for the reply schematic!

 

[OptsyEagle]

Do you have the gas set at full throttle (up against the neutral stop) and on one my older motors I have a little morning ritual where I pull out the choke, start it up, push it in 1/2 way, then all the way, then as it wants to die, I pull it out 1/2 way again, then back in and maybe do that one more time, maybe not and she is good to go. In other words I have to play with the choke a little. I am sure you have tried both of those suggestions, but if not give it a try.

My last thought would be the carb again. Also, I am not sure but from your video, but it did not seem like you had the motor submerged enough. It needs to be in the water to the level where the water is ABOVE where the water pump sits. It looked like your water was only slightly above the cavitation plate and your water pump might or might not prime at that level. It has nothing to do with your starting problem but something to be aware of.

 

[Moustache]

Do you have the gas set at full throttle (up against the neutral stop) and on one my older motors I have a little morning ritual where I pull out the choke, start it up, push it in 1/2 way, then all the way, then as it wants to die, I pull it out 1/2 way again, then back in and maybe do that one more time, maybe not and she is good to go. In other words I have to play with the choke a little. I am sure you have tried both of those suggestions, but if not give it a try. My last thought would be the carb again. Also, I am not sure but from your video, but it did not seem like you had the motor submerged enough. It needs to be in the water to the level where the water is ABOVE where the water pump sits. It looked like your water was only slightly above the cavitation plate and your water pump might or might not prime at that level. It has nothing to do with your starting problem but something to be aware of.

Yes the throttle is fully against the neutral stop. It wont start at all otherwise. I tried your choke trick and it worked between fully choked and half way. I removed the carb for what feels like the 5th time now and re seated the needle valve and spring (thinking i may have had the clip on the float arm wrong). Re installed the air mixture needle at 2 1/2 turns and now it would run for nearly a minute or two with the choke completely open. Pumps water from the little hole (telltale?) and idles pretty smooth. Then it bogs and dies again pretty abruptly. The choke wont even save it this time. After spending a few minutes fiddling with the mixture screw and pull starting it quite a few times it appears i broke the spring in the starter and now it wont retract the string. Headed to the marina tomorrow to get a new string and spring and maybe a new fuel valve which clips to the outside on the engine. This one feels like it has a very loose fit and may be letting air in the fuel line. Does anyone think this is plausable for what my engine is doing. I would have another video but the spring broke right before i was going to film it running again.

 

[schematic]

is it possible you used the wrong gasket when installing the top housing? I believe it comes with several.....

 

[Tim Frank]

Buy a $6- spark tester....or make one. Spark should jump a 3/8" gap ..... nice bright spark that makes a snap sound.
That will rule out ignition.

 

[Moustache]

is it possible you used the wrong gasket when installing the top housing? I believe it comes with several.....

I've checked to make sure the gasket i used was the right one. I've even switched between the original air mixture needle and the new one the plastic top came with.

 

[Moustache]

Buy a $6- spark tester....or make one. Spark should jump a 3/8" gap ..... nice bright spark that makes a snap sound.
That will rule out ignition.

thanks for the heads up, i'll pick up a spark tester while im out getting a new recoil spring

 

[Moustache]

The recoil spring has been reinstalled since the end slipped through the slot in the cup. Tested spark and was nice and blueish white with an audible snap. Noticed the ball valve kept losing pressure so i removed the fuel pump again to double check all of the gaskets and springs as per OMC directions and appears right and pumping. tested with the carb fuel line disconnected and saw little pulses of fuel coming from the line. The only thing along the fuel side which isnt new is the tank. So i guess that is next. Still wont run longer than about 30-60 seconds before dieng pretty suddenly. Any other suggestions would be great. I have no idea what to try at this point. I would hate to have a shop charge me for everything i have already done (carb rebuild, fuel pump rebuild etc.)

 

[raczekp1]

inside float chamber is small plasic pipe.
in my motor this pipe was cracked and at slow speed motor didnt get enough fuel.
buy 15 cm pipe at auto parts store and change the pine also

 

[Moustache]

inside float chamber is small plasic pipe.
in my motor this pipe was cracked and at slow speed motor didnt get enough fuel.
buy 15 cm pipe at auto parts store and change the pine also

Do you mean the small rubber tube that connects to the orangish plastic pickup? If so, i replaced that with the rebuild kit i got. or do you mean the orange plastic piece itself (the one that gets sandwiched between the carb body and the plastic bowl).

#2 in this diagram? The "nozzle well"

 

[bigmo65]

Mine had same symptoms, getting fuel and good spark. Went through the same stuff you did with negative results. Finally went with a new fuel pump from iboats for $43. Problem fixed. I think it was pumping fuel through the pulse port into the crankcase causing the motor to flood out after running a short time.

I read another post where OP rebuilt his pump and it would still die out. It took a new fuel pump to fix his also.

 

[raczekp1]

i had problem with tube (part no 4)

 

[Moustache]

Mine had same symptoms, getting fuel and good spark. Went through the same stuff you did with negative results. Finally went with a new fuel pump from iboats for $43. Problem fixed. I think it was pumping fuel through the pulse port into the crankcase causing the motor to flood out after running a short time.

I read another post where OP rebuilt his pump and it would still die out. It took a new fuel pump to fix his also.

The pump has been tested and is pumping. After checking the springs inside the pump, i found one that had shifted out of place. I got it running this morning and ran for nearly 10 minutes before stumbling and stopping. the tank is old (the gas is new) so i believe there are air leaks in the pickup tube or seal inside the tank. If nothing else works, i'll replace the pump. Thanks for the heads up!

Raczekp1: I replaced that tube with the omc rebuild kit and have made sure it is clear every time i,ve removed the carb.

it's really acting like i am having carb issues. so it's time to remove the carb again, find this "low speed idle jet" and clean it like it's never been cleaned before. also, does anyone have any advice or direction towards the small metal clip that hooks to the needle valve? How it is supposed to hook to the float arm (if at all).

Thanks for the help everyone!

 

[AlTn]

I don't believe it matters which direction that clip attaches to the float arm from as long as it's attached < older carbs that had the needle above the float didn't have one, but it does help insure that the needle comes off the seat >....as you've concluded, if it runs for 10 minutes then stumbles and stops, it seems to me it's running out of gas, out of spark, or, unlikely, overheating with possible water intrusion. When you have it running again, clip an inductive timing light to either plug wire and study the flash. I hope it continues to run for you w/o any problems, but if it doesn't and you have lost spark, your ignition is termed a UFI Ignition and is sorta notorious for acting up and causing symptoms such as you're experiencing. Post back with whatever happens next.

 

[Moustache]

I don't believe it matters which direction that clip attaches to the float arm from as long as it's attached < older carbs that had the needle above the float didn't have one, but it does help insure that the needle comes off the seat >....as you've concluded, if it runs for 10 minutes then stumbles and stops, it seems to me it's running out of gas, out of spark, or, unlikely, overheating with possible water intrusion. When you have it running again, clip an inductive timing light to either plug wire and study the flash. I hope it continues to run for you w/o any problems, but if it doesn't and you have lost spark, your ignition is termed a UFI Ignition and is sorta notorious for acting up and causing symptoms such as you're experiencing. Post back with whatever happens next.

Thanks! I didnt think it mattered which way it clipped on there. the directions from OMC and my Seloc manual both fail to mention what to do with that clip. It will only run the the throttle up all the way in neutral. If i try and bring it down to an idle. It cuts out and dies. If there was an idle screw on the carb body, i would adjust it. But there isnt. . . Even with the trottle twisted all the way it still seems like it idles a little low. I took some more videos over the weekend and will have them up this afternoon. I have an automotive timing light, can i use that? It has positive and negative clips though that i will have to hook to a battery i assume.

A new problem has risen as well after running it for a few minutes and spinning the prop, it started leaking oil from where the prop meets the white ring bolted to the gearcase. I assume it to be a prop seal. the manual shows two seals down there which is the next thing to replace i guess.

 

[AlTn]

if the engine is still in the tiller setup < not remote >, the knob at the end of the tiller handle serves as the idle adjustment as well as a stop if you are tolling at a certain speed, need to run to another spot, and then want to return to that trolling speed...in my experience, it takes some tinkering with that adjustment knob as well as the idle mixture screw to achieve a good idle...don't be surprised if you have to back the mixture needle out 4 or 5 turns from a soft seat to get things "in the ball park"....if what you are seeing coming from the prop area is black and thin it may just be unburnt fuel mix mixed with some carbon from the interior of the exhaust, this is common especially in engines that haven't been able to run for an extended time at wot while pushing a boat...

An automotive timing light works just fine and the + and - leads do clamp to a 12v battery...the clamp clips to a spark plug lead

 

[Moustache]

if the engine is still in the tiller setup < not remote >, the knob at the end of the tiller handle serves as the idle adjustment as well as a stop if you are tolling at a certain speed, need to run to another spot, and then want to return to that trolling speed...in my experience, it takes some tinkering with that adjustment knob as well as the idle mixture screw to achieve a good idle...don't be surprised if you have to back the mixture needle out 4 or 5 turns from a soft seat to get things "in the ball park"....if what you are seeing coming from the prop area is black and thin it may just be unburnt fuel mix mixed with some carbon from the interior of the exhaust, this is common especially in engines that haven't been able to run for an extended time at wot while pushing a boat...

An automotive timing light works just fine and the + and - leads do clamp to a 12v battery...the clamp clips to a spark plug lead

My tiller looks to be missing some bits on the end. all i have is the stop switch. there isnt even a spot to clip a safety lanyard. . . Not sure what's going on here or what exactly i am missing. Will take a photo and post later.

It is definitely oil. I've fixed a few engines with bad headgaskets and know the sight of oil mixed with water. It was a light brown oily liquid that leaked from the base of the prop and gearcase even while it was out of the water. This engine does not blow exhaust from the prop. 100% positive it is oil. I have a video of the leak as well. Just didnt bring the cord for my camera to work today so they will be posted this afternoon.