90 HP Issue

[kyudizky]

'84 90hp Johnson,
Issue:
Black exhaust coming from hub. Is this oil getting past a broken ring? not getting enough oil? Is there anyway to tell when the vro pump stops working, like will the low oil warning beep? What would cause it to idle fast on its own then didle down on its own upon cranking up. It would also idle up if I raised the motor at all.

Background Info:
Motor sat for exactly one month, took forever to crank again, but only the first time. Upon starting it idled high on its own and slowly came down to regular idle rpm's. Thought this was odd. ran fine on after that for 15 minutes (with muffs). Ran it again a few days later and started quick, did the same idle thing, but this time the exhaust was very black coming from hub. didn't run it long once i observed this.

All of this done on a hose with muffs.

On another note, because i'm paranoid, can a temp. gage be easily installed to be able to monitor engine temps or is that not necesary on an outboard with strong flow out of the tale-tell.

it has been extremely reliable motor (not cold natured at all) since aquired 6 months ago and ran almost everyweekend till a month ago (out of town for a long time). also, de-carbed and had an annual done, then ran one time, pretty hard, before it sat up.

Any help or direction appreciated

 

[kenmyfam]

Re: 90 HP Issue

Could be remnants from the decarb or just unburnt 2 stroke oil. Does it smell of gas ??? if so no worries. If it smells of rotten eggs then it is most likely lower unit oil. Then it needs further investigation.

 

[kyudizky]

Re: 90 HP Issue

I don't remeber a smell other than a typical exhaust smell. Strange thing is that it didn't smoke the first day i fired it up but did a couple of days later. Neither day did I put the boat in gear at all so i wouldn't think it was lower unit oil, but who knows. the grass is plenty black from it so I see if it has a smell when I get home. Any ideals on the strange idling?

 

[kenmyfam]

Re: 90 HP Issue

I don't remeber a smell other than a typical exhaust smell. Strange thing is that it didn't smoke the first day i fired it up but did a couple of days later. Neither day did I put the boat in gear at all so i wouldn't think it was lower unit oil, but who knows. the grass is plenty black from it so I see if it has a smell when I get home. Any ideals on the strange idling?

Can you give some more details on the idling issue. RPM, Muffs or in the lake etc.

 

[kyudizky]

Re: 90 HP Issue

All of this was on a hose with muffs. To get it cranked, I had the throttle engaged to give it a little gas to aid is cranking, nothing excessive. It cranked and was idling around 2000-2200 rpm best i can remember, then over about the 1 to 1.5 minutes, it slowly idled down to normal idle around 1000 rpm's. Before cranking i fixed a short in the tilt sending unit wired to the gage so after is idled down, just to check the triim gauge was working correctly, i tilted it up a little, and it would idle up more as i lifted the motor, lifted about a quarter of the way and went back down, so did the idle.

before letting the motor sit, i filled it full of fuel, only options was with ethanol fuel , but i did put the blue Stabyl ethanol treatment in the tank.

 

[kenmyfam]

Re: 90 HP Issue

The backpressure on the muffs is so different than in the lake I never really judge the reality till I am in a body of water. Mine typically idles high on the muffs but fine in the lake. Can you back it down a ramp to try it ?? no need to unhook the boat. Just have the motor submerged enough.

 

[tashasdaddy]

Re: 90 HP Issue

agree. 1984, if it has never been decarbed, it sounds like it needs it.

 

[kyudizky]

Re: 90 HP Issue

Tashasdaddy,
I am not sure if the motor had been decarbed before i got it. I would assume so because the motor ran to good since i bought it not to have been decarbed. Just before the boat sat for a month, I had a annual service done on the motor and the mechanic who did it said that it definetly needed a decarb , so the next day, i decarbed it per the directions on the Mercury Engine Tune bottle. I did this with the boat on the water so I could run it WOT afterwards as the directions suggested. Should I run another bottle of decarb through it? Would this cause the black smoke. I thought the carbon caused white smoke.

I was affraid to run the motor after it started smoking. I guess by your suggestions that it is ok too. If so, i plan on getting it in the water this weekend to see if she acts any different, i'm itching to bad anyways since it been over a month.

 

[kenmyfam]

Re: 90 HP Issue

Black smoke is burning carbon as the decarb solution does it's job. It will clear up as time goes by but initially it will smoke like crazy. It may or may not have been decarbed previously. Between decarbs your motor is actually accumulating carbon again and it will not really show in the exhaust.

 

[kyudizky]

Re: 90 HP Issue

assuming it needed a decarb badly, would it hurt to go ahead and decarb it again?

the strange thing is that after decarbing the first time, i ran the boat in the water, it didn't smoke more than normal, then flushed (saltwater) using muffs, again just normal amount of white smoke, motor sat for a month, cranked it on muffs (which took it a while to fire) and ran for 15 minutes, again normal amount of white smoke, ran again on muffs 2 days later, cranked fine but black smoked. I would agree that the black smoke is from burning carbon, but i wasn't decabing at the time. I assumed it was something else being that it didn't do it the several times after decarbing.

 

[kenmyfam]

Re: 90 HP Issue

Should be fine doing another decarb in my opinion. I used to decarb my smaller 2 stroke motorcycles every couple of weeks years ago to make certain that i had optimum performance. The fuel can only get in as fast as the exhaust gets out.