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1977 johnson 25 hp need help!!!

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michael8832

New member
i have a 1975 johnson 25 hp and im having trouble keeping it running.

back story- bought this motor of marketplace. it had compression and spark so i picked it up. long story short, after a minute of running the to spark plug is soaked in oil causing sputtering and misfires. every time i take it out and clean it, within a few seconds it starts up again.

i thought it might be bad rings, but the compression text holds at 120ish both cylinders. quick question, can compression be solid and still allow to much fuel into the cylinder? its only the top one. the oil mix is spot on, and I tried a few different cans to be sure. the bottom spark plug is clean and fires true every time. im sure its the only thing keeping it going.

i have found that my needle value is flattened and no longer a needle. could that be allowing too much fuel through my carb only affecting one cylinder? could it be leaf valve allowing too much fuel into the top cylinder?

if anyone has any advice i would really appreciate it. i was about to pull the rings, but I'm not sure that's necessary with it holding 120 compressions
 
Rings have nothing to do with this issue !!-----Check for a torn fuel pump diaphragm.----If torn install a new diaphragm for $10.00 or less
 
racerone said:
racerone said:
Rings have nothing to do with this issue !!-----Check for a torn fuel pump diaphragm.----If torn install a new diaphragm for $10.00 or less
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your the second source that suggest the fuel pump. i understand the compression of the pistons makes the diaphragm in the fuel pump work, but how would this mess with one cylinder?
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racerone said:
side note, i checked the pressure on both cylinders again. neither one loses compression and holds around 120. i have concluded that its not the rings as well.
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Time for you to look at this motor.----Inspect the fuel pump diaphragm.------Fuel pump is NOT driven by compression in the cylinders!----Fuel pump is driven by the crankcase compression of ONE cylinder.
 
I have a 1978 25hp evinrude and had a very similar issue once I replaced the power pack on my engine. For whatever reason the timing was going to opposite cylinders and was causing a very similar symptom. Once I swapped the ignition coils around the engine ran great. Might be worth a shot.
 
If timing was out be 180 degrees your 78 model would not run at all.------And a 1975 model as indicated in post #1 has a totally different ignition and the motor runs.----Trouble shooting on outboards is easy for me.----But apparently difficult to explain these days.
 
ok buddy, you seem to know what you're talking about. ill admit this is my first outboard, and it has been a challenge.

however, i changed out my fuel pump this week and had no change in behavior. (yes the fuel pump is installed correctly.) i agree it is a fuel issue since my carburetor cup is not filling. which lead me to believe something is stuck in my carb, or my pump is still not working. while watching the clear fuel line in installed recently, i noticed the fuel flowing backwards towards the fuel pump. i filled the line again and watched the fuel recede. on the third time i removed the hose from the tank entirely. the fuel continued to recede. there is a leak at the connection point where the fuel line connects.

once again im a beginner at outboards but, does this sound like the cause of my carb not filling? an air leak in the fuel line causing the pump to fail?
 
michael8832 said:
ok buddy, you seem to know what you're talking about. ill admit this is my first outboard, and it has been a challenge.

however, i changed out my fuel pump this week and had no change in behavior. (yes the fuel pump is installed correctly.) i agree it is a fuel issue since my carburetor cup is not filling. which lead me to believe something is stuck in my carb, or my pump is still not working. while watching the clear fuel line in installed recently, i noticed the fuel flowing backwards towards the fuel pump. i filled the line again and watched the fuel recede. on the third time i removed the hose from the tank entirely. the fuel continued to recede. there is a leak at the connection point where the fuel line connects.

once again im a beginner at outboards but, does this sound like the cause of my carb not filling? an air leak in the fuel line causing the pump to fail?
Click to expand...
The Oracle (Racerone) knows, Michael. But based on what you are describing, me thinks you need to first pull carb, take apart and soak parts for 24-48hrs in your favourite toxic substance (ex paint thinner) paying special attention to condition of bowl, float, needle and needle passages. Finish the treatment off with carb cleaner sprayed through all orifices. Ideally you would also remove the Welch plugs and inspect in behind but that would require buying a carb kit - if it were me and it was that vintage I would be ordering.
 
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