Johnson 120 looper power loss at low rpm then smooths out please help urgent!! please

[Skyla316]

1985 Johnson 120
Compression: 123/123/130/130

OK I had the plastic carb warpage an then I took the carbs of my donor 1992 120.

They are a different part number but compared the internals of the bowls internals an only part no that is different was the needle/float valve assembly (the needle spring clip an screw)

The donor carbs mounted perfect on my 85 120.

Took the boat out an at WOT is has loss of power for first 7-8 seconds an then boom it smooths out an starts to plane.

I almost thought a plug wire popped off but then it started smoothing out.

So my concern is maybe even tho the needle valves looked like the same size that maybe they actually are not an either causing a fuel restriction at start off or too much fuel?

It does have a hard time starting up as well an have to choke it.

Other thing maybe is the disconnected vro maybe is not blocked off properly? The tank has been removed an I don't not know the history of it except rebuilt carbs, new plugs, newer coil packs, lower unit seal kit an impeller that I just did

Please I'm trying to get this running before my father gets out of the hospital in a couple days as he just had multiple strokes an need him to enjoy some time out on the water.

Thank you all!!!

 

[racerone]

Re: Johnson 120 looper power loss at low rpm then smooths out please help urgent!! pl

Why would the inlet float valve be a different size / capacity on a newer 120 HP ??-----I think you need top look elsewhere for the problem.----Run with a timing light and see how spark behaves on all 4 cylinders.

 

[175se]

Re: Johnson 120 looper power loss at low rpm then smooths out please help urgent!! pl

Racer, could it be a big bore small bore issue? Even if the carbs bolt up there is a diff in the jets I believe. Ive run into this before with jetting issues with bridged vs single exhaust.

 

[Skyla316]

Re: Johnson 120 looper power loss at low rpm then smooths out please help urgent!! pl

Just went on ********** to compare part no an jet #s an all 3 are different between my 2 120 motors, so tomorrow I'm going to change all 3 over cause my engine is running like crap an barely gets on plane an while trying to do so an after it does it cuts in an out almost making me think I had an electrical problem but I spark tested all coils an they are strong but in my factory manual it does tell me how to adjust the spark advancement (cause my brother started messing with it in this process an now I believe its out of time) the manual doesn't say "the factory setting is x turned from all the way in or out" so I'm lost as where to start from or does that adjust of sound an feel under load in the water??

Again everyone thank you for your help its very much appreciated, I love this website.

 

[James R]

Re: Johnson 120 looper power loss at low rpm then smooths out please help urgent!! pl

I dont know what manual you have but most even Seloc and Clymer have initial settings for carbs however I dont think you have adjust ments on those. I will check.If there are adjustments and initial sets they are usually found in the carbs or maintenance sections. Sounds like a link and sync is necessary also. Do it all and dont miss any steps. Dont ignore the fuel pump and fuel lines from the tank. Did you clean and rebuild the replacement carbs.

 

[Skyla316]

Re: Johnson 120 looper power loss at low rpm then smooths out please help urgent!! pl

Not carb adjustment, the advance spark screw under the flywheel. Carbs rebuilt, checked all fuel lines.
I did notice yesterday when we were all full speed an engine was cutting in an out that the fuel gauge an rpm gauge would drop at the exact same instant the cut out happened.
Mentioned in another thread for a float bowl issue I was advised that since the carb swap out was from a different year he noticed the bore size was different so I was told to use my original jets from my junk carbs an swapped them out today an dropped my motor in my 100 gallon trail an still running like crap but seemed to start up easier. I'm thinking its really out of time.

 

[James R]

Re: Johnson 120 looper power loss at low rpm then smooths out please help urgent!! pl

The screw you refer to is important for idle but it must be adjusted and then the carb/timing synchronization must be done. Follow you manual for this. Start the motor and get it warm. Stop the motor. Release the carb linkages so that both Carb butterflies spring fully closed. Leave loose and restart the motor. Adjust the the timing screw to run the motor at about 1100 RPM out of gear. Stop the motor and lock the screw. You now need to tighten the linkage screws with the throttle cam free ensuring that the butterflies stay in the closed position.
The rest is simply making cam adjustment t bring the marks into line. Check you manual for the full set up.