1989 johnson 120 runs 2500rpm at full throttle

[Solittle]

Re: 1989 johnson 120 runs 2500rpm at full throttle

Before spending a bunch I would check to see that you are gettijng good spark from all cylinders. By that I mean with a spark testor and getting a bright blue snap that jumps at least a 1/2" gap. Also your description of the way you cleaning the carbs is far less than the steps recommended. There should be a sticky or search on how to do it.

I'm not sue that your 89 has the 2,500 rpm slow feature. My 87s do not.

 

[buggyman20]

Re: 1989 johnson 120 runs 2500rpm at full throttle

I bought a Johnson shop manual for this motor and the way it tells you to clean the carbs is the way I did it. They are plastic so you can not soak them in anything. Clean the jets and change the float valve, check the float measurement and new gaskets. Blow out all holes with carb cleaner. I took the boat out today ran great for a while then it started to spit and miss a little. At a slow idle about 1800 rpms it just quit like somebody turned it off. When I tried restarting it would spit and sputter and then it would just turn over with no results. I trolled back to the launch. tried starting it again and after several attempts it finally cranked up. With the fast idle up to about 2000 rpms it just quit again. I got it started put it on the trailer and ran the motor up to 3500 with the gearshift and it ran solid. I did notice a small leak where the hoses come out of the valve that goes to the tell tale. My water pressure ranged from 5 psi at idle to almost 20 psi at 5500rpm. The temp gauge which is mounted on the port head would read 170 at idle and then drop to 100 at the higher rpms. When I went back to idle or slow the temp would go back up.

 

[reeldutch]

Re: 1989 johnson 120 runs 2500rpm at full throttle

when it acts up , do a cylinder drop test.

meaning , get plastic pliers and pull a sparkplug wire off and listen to the engine, if it changed rpm your cylinder is contributing. if it didnt change rpm the cylinder is not contributing.

you might this way narrow it down to a cylinder or 2.
if you have no spark rouble shoot ignition.
and yes its starting to sound like a bad pp.

 

[buggyman20]

Re: 1989 johnson 120 runs 2500rpm at full throttle

One post said maybe the fuel pump but the bulb stays hard all the time. Does it pump gas into the carbs or is that done by vacuum? Also I thought about the issue with the temp gauge. Would you think with it hooked up to the power stud on the rpm gauge that it would affect the temp gauge? The only problem with checking the plugs is when it acts up it has to be running at high rpms. Is there a way to check the power pack with out a special neon test light? Like I said I have a Johnson manual for that motor so I have instructions. I will keep you posted.

 

[reeldutch]

Re: 1989 johnson 120 runs 2500rpm at full throttle

run the boat until it fails bring it back to the trailerput it on the trailer.
with the car in park and parking brakes on run the motor in gear above 2500 rpm.
if it acts up do the cylinder drop test.

you will have to verify that it is indeed a ignition problem.
or spend the money on a powerpack.

a neon test light is about 20 dollars or so.
it will flash at you when it gets spark.
same does a timing light.
it doesnt check if your cylinder is contibuting.
when you pull a wire of you check for ignition and fuel and compression all at the same time.
make shure when you pull a wire hold it close to the block so it if it has juice can jump to ground. you should hear it sparking.

 

[buggyman20]

Re: 1989 johnson 120 runs 2500rpm at full throttle

can power packs go out when they get hot from the engine or do they usually just go out all at once?

 

[reeldutch]

Re: 1989 johnson 120 runs 2500rpm at full throttle

that is a possibility.
you have to test it or buy a powerpack.

 

[ezeke]

Re: 1989 johnson 120 runs 2500rpm at full throttle

I'm not sue that your 89 has the 2,500 rpm slow feature. My 87s do not.

The 1989 120 and 140 motors have QuikStart and S.L.O.W.

 

[SparkieBoat]

Re: 1989 johnson 120 runs 2500rpm at full throttle

I am still suspect of the power pack..

 

[crabby_bob]

Re: 1989 johnson 120 runs 2500rpm at full throttle

FYI my brother and I are having a similar problem with our 1988 120 hp johnson. We suspect slow mode is kicking in but can't figure out why. The motor runs fine at both high and low RPMs but if we troll for about 30 minutes we can't get the the motor above 2600 RPM unless we shut it off and let it sit for 5 to 10 minutes. Have you tried that?

I don't know if this helps you but here's what we've done. We changed the impeller, as you did, and it didn't help. We also tested the temperature sensors and found that the port side sensor was bad. We changed it but it didn't help. We then tested the alarm system including the horn, the sensor wiring, and the bypass diode and the system checked out OK. So we're at the point where we still feel it's going into SLOW mode and are trying to figure out how the mode is getting triggered without the alarm sounding. I'm beginning to suspect either the power pack is faulty, or the temperature is rising to just below the trigger threshold of the sensors, which I believe is 203? F. My theory is that that the sensors might be toggling on and off too quickly to sound the horn, but slow enough to trigger SLOW mode. Our DVMs have a tone setting for checking continuity and I noticed that when we tested the sensors the tone would be unsteady until the switch had been above 203? F for a second or two.

We monitored the motor temperature while running at both high and low RPMs and neither bank got above 155 degrees but the problem didn't occur during the test run. That might have been because it was late in the year and the water temperature of the pond had dropped to about 50? F so we've put the boat away for the winter and will start troubleshooting it again in the spring.

 

[buggyman20]

Re: 1989 johnson 120 runs 2500rpm at full throttle

When I put in the impeller I also put in a water pressure gauge. I also checked the therms to make sure they were working. After thinking about it and talking to some other people it seems the motor runs great for about 15 to 20 mins and then starts missing. I had one person suggest to run it without the motor cover. He had a friend that had the same problem with the cover on but no problem with the cover off. Also I will run it until it acts up and then fish for an hour or so and see what happens. I am able to repair almost anything but with this motor you have to have a PRV and some other specialized equip. that is expensive. I will check what I can and if I can not fix it I will have someone do a diagnostic check to find the problem. I will let you know what happens.

 

[ezeke]

Re: 1989 johnson 120 runs 2500rpm at full throttle

On your engine, S.L.O.W. is controlled by a single tan wire that runs to the powerpack. It has a single bullet connnector that you could disconnect for testing if you are sure that neither bank of cylinders is overheating.

It is possible that you may have a short in the wiring or that the blocking diode has failed.

 

[buggyman20]

Re: 1989 johnson 120 runs 2500rpm at full throttle

I do not have a overheat problem now since I changed the impeller. My problem is after running a while it starts missing and at a slow speed it just quits like someone turns the key off. I am going to do what tests I can. Any ideas will be helpful.

 

[SparkieBoat]

Re: 1989 johnson 120 runs 2500rpm at full throttle

so your motor is not limited to the 2500 rpm now?? have you replaced the spark plugs?? i had a real problem motor once and plugs looked fine but when I replaced them it quit shutting off while idling and ran smoother at all throttle positions

 

[SparkieBoat]

Re: 1989 johnson 120 runs 2500rpm at full throttle

with the cover off you can visually inspect carbs while running, look for the same spray pattern in each carb if one has less spray (or too much) it may need to be cleaned. I run my motors with out the carb cover all the time, they just seem to run better. also have you got a spark gap tester and tested each wire??

 

[SparkieBoat]

Re: 1989 johnson 120 runs 2500rpm at full throttle

you also could be getting water in your fuel tank..you need to inspect your fuel and look for milky or signs of water. also clean/replace your water fuel separator filter.

 

[ezeke]

Re: 1989 johnson 120 runs 2500rpm at full throttle

You should not run a big bore looper for long with the air silencer cover and baffle off the carburetors.

 

[SparkieBoat]

Re: 1989 johnson 120 runs 2500rpm at full throttle

why not Ezek??? I was not aware that it could be a problem. I run it with only the carb cover off, but with the cowl in place. If I am risking any kind of damage to my motor I will certainly stop.

 

[ezeke]

Re: 1989 johnson 120 runs 2500rpm at full throttle

why not Ezek??? I was not aware that it could be a problem. I run it with only the carb cover off, but with the cowl in place. If I am risking any kind of damage to my motor I will certainly stop.

See: http://forums.iboats.com/showpost.php?p=1455534&postcount=13

Also, don't set the idle with the air cover off - see linkage and synchronization (section 1) in your service manual.

 

[SparkieBoat]

Re: 1989 johnson 120 runs 2500rpm at full throttle

great post ..thanks Ezek..i will re-install my carb cover...works great on my older motors though with out the cover