Mid 90s Johnson 115

[Bspaulding]

I recently bought a mid 90s Johnson 115 2-stroke to put on my 72 Grady White. I have replaced the fuel pump, starter, and head gasket, changed the spark plugs, and water pump. It runs fine in the driveway on muffs (throttles up/down and goes into gear and runs), but as soon as I get it into the water, it is difficult to start and if I have the choke up, it goes WFO (wide effin open) but as soon as I put the choke off, it bogs down and dies. I have taken it out and usually have to use the primer solenoid to make it out of the ramp and even at full throttle sounds like it’s bogging down and has little power. I took off the carbs and cleaned the bowls out but didn’t clean out the fuel lines. Any suggestions for why this is happening? I am attaching a video of it idling on muffs. I have seen this question posted on other threads but I have not come across a solution for my engine so far. I have also not done a compression test but engine does not sounds like it’s missing. I have run seafoam through it and it did not change anything. The smoke in the video is off of a oil rich mixture about 45:1 of oil and ethanol free 93 octane.

Also, I have been a gas/diesel mechanic for the past 15 years or so working on heavy equipment. I am mechanically inclined but this is the first time I’ve owned a boat and have worked on a boat motor.
View attachment IMG_4155.MOV

 

[racerone]

The lever that you raise is NOT THE CHOKE at all.---It is the warm up lever to raise RPM with no shifting.------You push the key in while cranking to start this motor.----And best to do a compression test.----Post your numbers.----

 

[Bspaulding]

The lever that you raise is NOT THE CHOKE at all.---It is the warm up lever to raise RPM with no shifting.------You push the key in while cranking to start this motor.----And best to do a compression test.----Post your numbers.----

Got it. Thank you for that I assumed it was the choke. I usually have to push the key in for the primer solenoid to kick in while starting.

 

[racerone]

The primer solenoid is a VALVE that opens when you push the key in.------While cranking the fuel pump then pushes fuel through this valve.-----This fuel goes directly into the intake airstream for cold starting.----This fuel bypasses the carburetor float bowl and metering circuits.----The primer solenoid is a wonderful item that has replaced inefficient choke flapper plates.

 

[Bspaulding]

The primer solenoid is a VALVE that opens when you push the key in.------While cranking the fuel pump then pushes fuel through this valve.-----This fuel goes directly into the intake airstream for cold starting.----This fuel bypasses the carburetor float bowl and metering circuits.----The primer solenoid is a wonderful item that has replaced inefficient choke flapper plates.

Just did a compression test. 3 of the 4 cylinders were at 90 +/- 3 and one cylinder was around 70. The cylinder that was at 70, I recently replaced the head gasket for because there was a leak. Attached is photo of old gasket. Bottom cylinder was 70 psi

 

[racerone]

Are you saying it is at 70 PSI now with a new head gasket ?

 

[Bspaulding]

Are you saying it is at 70 PSI now with a new head gasket ?

Yes. I did the compression test at idle throttle after the engine warmed up for about 20 minutes. Did not put it all the way open.

EDIT: After reading more about performing compression checks, I will do another one tomorrow and post results. I did not pull all spark plugs out at once but did each one individually and put it back when done.

 

[racerone]

Well with 70 PSI compression you have a bad gauge or a motor that needs big $$$$$ work.

 

[Bspaulding]

Well with 70 PSI compression you have a bad gauge or a motor that needs big $$$$$ work.

I had just bought the gauge prior to doing the test so I don’t think it’s that. While I have the head off, I inspected the cylinder and cylinder wall and did not see any gouges or scratches in them. This motor was pulled off a old project boat and had been sitting for a while.I am going to get some engine tuner and spray it in there And see if they can break down any carbon buildup that’s on the piston rings and bring the compression up. I have read great reviews over the Johnson and Evinrude engine tuner spray and will try that before breaking the motor down. Has anyone else used this product?

 

[Bspaulding]

I had just bought the gauge prior to doing the test so I don’t think it’s that. While I have the head off, I inspected the cylinder and cylinder wall and did not see any gouges or scratches in them. This motor was pulled off a old project boat and had been sitting for a while.I am going to get some engine tuner and spray it in there And see if they can break down any carbon buildup that’s on the piston rings and bring the compression up. I have read great reviews over the Johnson and Evinrude engine tuner spray and will try that before breaking the motor down. Has anyone else used this product?View attachment 330367

Well, I sprayed this in directly through the carbs throats while the engine was running just as suggested then let it sit for about 30 hours and ran it for 10 minutes or so at slightly above idle and redid the pressure test. Pulled all the plugs out and it brought the previously 70 psi cylinder up to around 85-87 psi, and the other previously 90 psi cylinders up to around 93-95. So now they are all within 10 psi of each other. I changed the plugs and I put it in a bucket to test it with some back pressure and it seemed to have improved drastically. Will take it down to the river tomorrow to see it it’ll idle good at the dock.