'93 Johnson 25HP, Can't get it to idle right...VIDEO!!

[tucker99]

Carb rebuild, twice, good spark, good compression, bad plug wire so replaced both. Can't get it to idle right. Any ideas guys? Thanks!!

https://www.youtube.com/watch?v=qbV4Nt5Uw88&feature=youtu.be

 

[smoke33]

I have the same engine same year but pull start and have the same issue going. I pulled off the fuel pump to access the fuel screen and it had some gunk in it. I cleaned it out and was a little better. I did notice the diaphragm in the fuel pump was not in the best of shape so I just ordered a rebuild kit for it in hopes that will fix it. I look forward to reading responses from others who know more than me.


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[nccatfisher]

Before we get into a bunch of obvious questions let me ask just one. How fresh/clean is your fuel? I had a motor just like that, it almost made me pull my hair out. Turns out my "fresh" fuel although very recently bought was contaminated. Changed it out, drained the carb and lines and readjusted everything and it ran like a top. It ran/idled just like that no matter what I did before I found the issue.

 

[maintenanceguy]

Random thoughts:

Seems to be hunting when at idle. rpm up, down, up , down. Often indicates a fuel delivery issue. Check tank, fuel lines, pump, vacuum that drives pump, filter, water separator, and fuel quality. If this stuff is original or older, I would replace everything from the tank to the carb.

Assuming the carbs are now good, it still could be the idle air adjustment on the carb - if that hasn't already been adjusted correctly. You'll need the factory manual to get the procedure to set that correctly.

Finally, the least favorite. How is the compression? a bad head gasket, scored cylinders, bad compression rings, etc will let the expanding gasses from combustion escape from the cylinder. At high RPM you are making a lot of expanding gasses so it doesn't effect performance a lot. At idle, when you're barely making enough to keep the motor running, these problems will make a big difference.

 

[GYPSY400]

Another thought is the thermostat.. it will be hard to tune properly if the engine temp is not consistent.

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[turbotodd]

don't know but I have been given the same motor, 25hp johnson, needs carburetor work. This carburetor looks like fun to remove. Electric start so the starter has to come off. Who's the idiot that designed this.

 

[smoke33]

don't know but I have been given the same motor, 25hp johnson, needs carburetor work. This carburetor looks like fun to remove. Electric start so the starter has to come off. Who's the idiot that designed this.

Not having an electric starter on mine it came off easy. I always said, the people who designed cars should be made to work on them. Then they could go back and redesign them properly.


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[tucker99]

Thanks guys...I have the FSM with a lot of greasy fingerprints on it. New fuel pump, fresh fuel,103 psi compression both cylinders, new plugs and wires, getting the spark to jump 7/16". I believe it's delivering fuel; primer has clear tubing coming from the bowl to the primer and I don't see bubbles. Tried pulling primer out just a bit to warm up mode and it definitely dumps fuel (bunch of gunk in the trash can). Yea, I've had the carb off twice, need to pull the starter, loosen manual starter, pull the solenoid, loosen clevis end throttle cable, PIA. You'll notice one of those digital tachs on the tiller arm; didn't work right out of the box. This situation is a little weird. When ice cold the engine runs fine and I can get it to idle. Last about 2-minutes and it starts coughing. The sneeze turns into a cough and it stalls when idled down.

 

[tucker99]

Yea, I replace the thermostat. I did everything you should do with an old motor an unsure of maintenance. Stat, plugs, water pump, and fuel pump.

 

[Pappy]

Wow.....lots of replies here.
Nowhere have I read what your initial needle setting is? ? ? Nor have I read a single suggestion that you start with the basics and adjust the mixture before diving off into things more complicated.
So......
I do not care what your initial setting is but what I want you to do is turn your idle mixture screw 1/2 turn counter clockwise and re-run your engine.
Let us know what effect this has.

 

[tucker99]

Will do that. Something I noticed that is not shown in the FSM. My carb primer output has a T. One hose goes to a nipple on the carb feeding the throat on the carb. The other hose goes to the intake manifold below the carb a little offset to the starboard side. The FSM shows a "oil recirculation hose" going to it. Wondering if this is a previous owner thing or was there a service bulletin the showed the modification? Original setting for the idle screw is 1-3/4 turns out.

 

[RaisedByWolves]

The hoses you describe are normal.

I’m going to take a guess at your problem and say you have a bad top/bottom seal judging solely on what I can hear on my ipotato video playback.

 

[tucker99]

Other than that sneeze. How to inspect/check for that other that pulling the power-head and splitting the cases?

 

[tucker99]

Ok, did some research and the classic symptom is difficult to start. My motor lights right up soon as I touch the button. Also, wouldn't a bad seal be evident in a compression check? I have 103-105 PSI cold engine on both cylinders. Also, no goo coming from under the flywheel. If the hoses are normal, how come they don't show it in the FSM? Thanks,

 

[tucker99]

However, the lower seal may be the culprit. My test tank has globs of oil floating in it.

 

[Sinkingfast]

Take Pappys advice before doing anything else....do it for yourself...don't worry about slime in the water or anything else now.

 

[RaisedByWolves]

Take Pappys advice before doing anything else....do it for yourself...don't worry about slime in the water or anything else now.

I forgot to watch the vid on a actual computer, but yeah, do the basics first.

But no, a bad seal or other crankcase leak will not show up on a compression test.

The exhaust ports are the last thing to close so compression does not begin until they’re closed.

 

[RaisedByWolves]

Finally got to watch this on my home computer.

Plenty of smoke yet its sneezing like its lean.

Have you had it on the water at more than idle during this?

What prompted the carb rebuild?

 

[double5]

As has been indicated on this thread, a leaky crankcase seal can lead to lack of "pre-compression". Two strokes pressurize the crank case on the downward piston stroke so that it can be taken into the intake port and ignited on the upward stroke (where your "normal" compression test reads"). You can use soapy water sprayed on the outside of the case, upper seal etc. and monitor while cranking. I would do it with the ignition disabled. If all is good, the reply about the lower seal could be it and it would require the powerhead removal to test that. That stuff has driven me crazy before and that is the only reason I am a bit familiar with it. Do all that after checking the idle adjustment etc.

Hope that helps.
Jeff in GA

 

[Sinkingfast]

I believe the intake port is from the carb to the reed valves or piston if piston port. Then crankcase to the transfer port (cross flow) or loop ports and in to the cylinder.

Most 2cy single carb outboards have asymmetrical respiratory systems..each jug will not tune exactly the same..even with perfect seals and all. Take a warm running outboard engine at low speed and start turning down the low speed needle. One jug will start misfiring before the other jug.

It could be just the case here...might just need a turn of the needle...

I get crap in the water with my 4 stroke 2.5hp motor in a barrel so pay no attention to the nasty water.