# 90HP Johnson running rough



## BassMaster19 (May 22, 2008)

Hey guys i currently bought a bass boat with a late 80's 90HP johnson...ran fine, idled fine and really ran good in the upper RPMs. Well i took it out the other yesterday and it started right up and idles fine but when i give it throttle it sounds like the exhaust has gotten louder if that makes sense? and it dosent rev as quickly or smoothly..ive had it out all summer with 0 problems and now its kinda acting wierd. The first thing i noticed was the increase exhaust sound..atleast thats what it sounds like to me. anyone have any recommendations about where i should start to diagnose it? Thanks.


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## oarfish (May 12, 2004)

Clean and rebuild the carbs on any used outboard motor before you put it to use.
Small amount to spend and it should be done anyways.
Might even takes care of your problems. It is kinda like a tuneup for a used car.


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## BassMaster19 (May 22, 2008)

I work on motors all the time (atvs,cars, small motors) but this is my first boat motor..is there a how to anywhere online for this specific motor? Thanks.


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## slimdaddy45 (Aug 27, 2007)

You didnt blow a head gasket did ya or the base gasket dont know of anything else that would make it louder


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## BassMaster19 (May 22, 2008)

im not sure..i was crusising across the lake pretty fast and then when i came back to an idle it sounded kid of wierd. Im not sure if its louder or if its just running rough which is making it bog and sound different. I dont see why it would randomly just start running wierd.


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## bountyhunter (Apr 28, 2004)

pull the plugs see if one is way differant in color than the rest, if so put four new ones in, and start using a better grade of gas , a can of sea foam will always help. it,ll clean the gunk as you run the engine. if thats not a fix get a hold of johnrude on here he,s a good motor man.


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## BassMaster19 (May 22, 2008)

i plan on pulling the cover off and checking stuff out on Monday..anyone else have any input? Thanks.


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## Marinette Sportfisherman (Apr 13, 2010)

get a 6 gallon tank and try it on a fresh seperate fuel source first. Ive seen fuel pick up or even a bad prime bulb cause issues start simple then work into the carbs or plugs.


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## PromiseKeeper (Apr 14, 2004)

maybe worth a try?

http://www.outboardrepairs.com/johnson/


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## BassMaster19 (May 22, 2008)

Well guys i haven't had much time to look at it..i did pull the plugs tho. I took a picture of both blugs from each side of the motor. Let me know how they look.


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## UFM82 (Apr 6, 2004)

Maybe a little rich- plenty of carbon on the plugs. A good decarbon job may help with the run issue if the inside of the engine is goopy. Try this deal:


This works for Carbed, EFI, Ficht, HPDI, Optimax and even 4 strokes...
First you need a separate small fuel tank. One of those 3 gal red Tempos works great or an empty gal milk jug will also work, but might be a bit messier..

I use Seafoam over the OEM stuff like OMC Engine Tuner or Merc Power Tune because in the last few years they changed the formula and you have to let them sit up 12 hours. Who's got time for that?? Seafoam you can buy from NAPA, CarQuest or other auto stores. Seafoam works in 15 mins.

You'll need 3/4 gal of gasoline and one 16oz can of seafoam for each engine. Don't forget to add 3oz of oil if you are premixing in a carbed engine. Use about 3 ft piece of fuel hose off the little tank. You connect this tank to your engine by pulling off the main tank fuel hose off the intake side of your water separating fuel filter and plug the hose off the small tank on to that fitting. Or you can separate the fuel line on the tank side primer ball, so you can still use your primer. If you have an engine that has fuel plug then you need a fuel plug on the little tanks hose.

Start the engine, let it warm up and start pulling the mix into the engine. You may have to increase the idle to keep it running once she get loaded with the Seafoam. Run the engine 15 mins in the dock or just cruising around under 2500. Then shut it down and let it sit for 15 mins. Restart the engine, the smoke you see is the carbon burning off. Do the whole thing again and let her sit again for 15 mins. If she smokes after the second time do it again, but I've never seen one still smoke after three doses. The gallon mix should be enough to do this 3 times. You don't need any wide open throttle, you don't need to change the plugs. If it's cleaning the combustion chambers it's also cleaning the plugs, but every 50-60hrs is good time to change plugs in most engines.

I cleaned a antique evinrude one time that had a 1/4" of solid carbon on the exhaust chamber walls by running a 1/2 gal of the mix through it. Seafoam has been around since the 30's and it's what they used when they were burning straight 4 stroke 40SAE oils in outboards. 

You guys with the 4 strokes think you are immune from this? Those engines work 10 times as hard as any auto engine ever will and they will carbon up. I bought a Bronco two years ago that had 95,000 miles on it. When I used seafoam on it I had the neighbors hanging out of their front doors looking for where the fire was after I started it the first time there so much smoke.

Too many are under the assumption that it's totally the 2 stroke oil that causes the carbon, Wrong... it's also the additives they put in the fuels today. The carbon inhibitors in 2 stroke oil are there for this reason also. Remember when gasoline used to smell like gasoline, today it smells more like bad cologne.

For those guys that like to do the carbon treatment by spraying it down the carbs Seafoam also comes in spray can called Deep Creep. It's the same stuff under pressure. Says right on the can Oxygen Sensor Safe, for you Yam guys.

After that if your engine maunf recommends a daily additive treatment then do that in the mean time, but all 2 stroke outboard need decarboned every 50-60hrs. If I owned a 4 stroke I would do it the same. Once you are set up with the tank and hose the Seafoam is only 5-6 bucks can. It to easy not to do it


As for the sound it make be that the engine is working harder because it's not producing the hp it used to and you are pushing it. Don't know about that. If you have gasket issues it will cause a myriad of problems. Notice any unusual smoke or oil/gas residue anywhere?


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## BassMaster19 (May 22, 2008)

no i haven't noticed any unusual smoke or anything (other than the normal smoke) im gonna put new plugs in this week and run it on the muffs and see if the sound is still there. Ill get a video.


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## markfish (Nov 22, 2007)

thats a good report,and if i may add to it i would change the plugs and run a higher gas like marathons fuel 93,has only 2 percent eathenol,hope i spelled that right but i think you get the picture,and after running the seafoam i alwise run stabil in my motor all season,keeps it clean markfish


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## freyedknot (Apr 10, 2004)

how old are those plugs anyway? they look like they should have been replaced a year or 2 ago. plugs are cheap insurance for a good running motor. i replace mine every spring.


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## BassMaster19 (May 22, 2008)

I'm not sure..i bought the motor at the beginning of this summer..so who knows. I should have checked them sooner. I'm not too familiar with 2 strokes, but it appears they r pretty hard on plugs lol


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## UFM82 (Apr 6, 2004)

The plugs are fine- just dirty. If the gap has widened you can regap them unless the center electrode is worn. Then it's time to replace. At a couple of bucks each it's not a big expense. Why replace if they are simply dirty? Do you buy a new car when it gets dirty? Don't mean to be offensive but unless you have physical wear/damage on the plug itself there's no reason to replace them. 


And anymore most manufacturers advise against using a higher octane fuel than recommended. 87 is fine for most normal (non-high performance) outboards and high octane fuels can cause damage due to higher cylinder head temps, especially on older engines. Find out what Johnson recommended for that engine. I'll bet the manual says 87.


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## BassMaster19 (May 22, 2008)

Here is a video from my phone of the motor running on Muffs..you can see it dosent rev as fast as it should.

[ame="http://s33.photobucket.com/albums/d75/atvkid4eva/?action=view&current=IMG_0489.mp4"]IMG_0489.mp4 video by atvkid4eva - Photobucket[/ame]


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## BassMaster19 (May 22, 2008)

just click the top of that box to watch the video


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## BassMaster19 (May 22, 2008)

Any Input on the video?


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## I Fish (Sep 24, 2008)

I think I would check to make sure all of your plugs are firing. It sounded to me like a miss, plus it seemed like a lot of smoke, surely more than my 100 Evinrude makes on muffs. Looking at the picture of your plugs makes me think this as well.


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## BassMaster19 (May 22, 2008)

Okay, Whats the procedure to check to make sure they are all firing?


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## BassMaster19 (May 22, 2008)

The only way i know is to set the plug against the block and turn the motor over..is there a better way? maybe i have a bad coil.


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## BassMaster19 (May 22, 2008)

if i get a spark tester what do i set the gap at for this motor? Ive been reading 7/16" is that right? thanks!


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## BassMaster19 (May 22, 2008)

okay guys i have some news. I ran a compression test and all the cylinders were between 115 and 120 PSI so that is not the issue. I also ran a spark test and the bottom right plug wire barely has any spark at all. So does that mean my coil for that cylinder is bad? That has to be the reason that the motor is being sluggish. Let me know what you guys think. Thanks!


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## UFM82 (Apr 6, 2004)

Bad wire, bad plug, bad coil. If you have a dead cylinder it will change the tone of the engine and that may be the sound you are noticing. And that would explain the sluggishness and slow-revving. Go backwards- cheap first. Change the plug, then the wire, then the coil if needed. 

Good to hear the engine is in good shape- that's always nice to know. LOL


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## BassMaster19 (May 22, 2008)

when swapping coils to see if the one was bad i noticed that the bottom of the one coil without spark was melted somewhat causing it not to ground properly when it was bolted down. Cleaned it up and re bolted it up and it now has spark! seems to rev a lot faster too on the muffs. Gonna test it out tomorrow at portage lakes. Will report back!


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## BassMaster19 (May 22, 2008)

UPDATE**

Okay i took it out on the water last night and it still is not running good! Idles fine, but its like even with the throttle pinned it only revs about half throttle making it never plane. It revs to the sky when its on the muffs, but not in the water..any other ideas? What else can i do to troubleshoot. Thanks!


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## keepinitreel (Apr 11, 2004)

You might want to replace the thermostats or at least check them. I had a similar problem,replaced them, and it ran fine. 
Also did you check all fuel lines, and then do a carb check.
My last two issues were carb. due to bad gas (ethanol)


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## BassMaster19 (May 22, 2008)

where are the thermostats located? and how would i check them?


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## keepinitreel (Apr 11, 2004)

I would highly suggest getting a service manual. Seloc should do the trick and for your $30 investmant you can learn alot and save$$.

On the cylinder head is where you will find the stats, one on each side. You might want to search online to find out exactly. I checked mine on the stove with a pot of water and thermometer. The temp it opens should be stamped on thermostat.


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## BassMaster19 (May 22, 2008)

I'm very familiar with motors, just not to much with 2 stroke motors. From what i know a bad thermostat will cause it to overheat, why would a bad one effect its performance?


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## peple of the perch (Sep 13, 2004)

you dont want to rev a motor to high with muffs on because there is no load on the prop or the gears and can cause sever problems in the LU.


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## BassMaster19 (May 22, 2008)

Okay i only did it one time very short. Anyone have more info on why a bad thermostat may cause my issues?


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## fish on! (Oct 15, 2009)

I am probably the least knowledgeable person here, but if a thermostat is stuck OPEN you won't maintain operating temps.


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## BassMaster19 (May 22, 2008)

The only way to test them is removing them and boiling water?


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## fish on! (Oct 15, 2009)

This will tell you if it's functioning, but not at what temp.I used to check them on the stove with a candy making thermometer. (very cheap item)


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## fish on! (Oct 15, 2009)

As stated before, I'm no expert, but am in the process of trying to become as knowledgeable as possible. While doing research I came across this in an article, I'm not sure if it applies, but it's something to consider. 



"A condenser is simply a lot of aluminum foil wrapped between waxed paper as an insulator. If the paper starts to deteriorate, after running for a while, the metal will heat up & expand. IF this happens in a location where the insulation is bad the metal shorts out to the next wrap, nullifying or shorting out & no output is achieved. But IF this is the case, many times when the condenser cools down, the short goes away until it warms up again. Once it has done this process a few times, then the short becomes rather permanent & the condenser is inoperative

If that driver coil (under the flywheel) starts to fail, is cracked, or starting to melt down, or whatever, there is a possibility that it would also operate when cold, but fail by shorting out when heated up by the running of the motor. However do not just replace them because they are oozing black tar like goo. They may still run for some time."


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## BassMaster19 (May 22, 2008)

Thanks for the help! Has anyone else had any symptoms of bad thermostats causing it to not rev high when in the water??


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## BassMaster19 (May 22, 2008)

okay, so i think im going to buy a carb kit, thermostat kit and 4 new coils. How hard are the carbs to 
clean and rebuild the jets? ive worked on many 4 stroke carbs..


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## keepinitreel (Apr 11, 2004)

Before you invest in a carb kit, check and see if the original parts are still good.
It will save you$$


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## BassMaster19 (May 22, 2008)

okay, will i need any gaskets for reassembly? and nothing will come out of adjustment by just removing and cleaning correct?


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## keepinitreel (Apr 11, 2004)

Nothing did with my yammi but it is a 2001. You have to carefully inspect and make sure they will seal 100% and all other parts are not worn.


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