Johnson 90 Oops it did it again

[That old Mercury]

Hi All
I have put roughly 100 miles on a new to me boat. And installed complete fuel system, water pump, thermostats, spark plugs, 2nd carb kit.
Since i have had the issue of it bogging down when it hits a boat wake.
Well i hit my first boat wake yesterday in that 100 miles of No problems and instantly while throttle was 3/4 wide open it bogged down so quick i lurched forward standing up and it threw my personal oxygen pump off the bench seat and into the boat! because it went from 29 mph to 9mph!!
Switched it off killed all the power for a few minutes.
Started up instantly and idled fine.
Could push the throttle wide open and could only get about 1500 rpm and right at 9 mph.
Being boat ramp was roughly a mile away ran it wide open at 9 mph to see if it would improve, it did not, but it did use up at least 3 gallons of gas in the mile.
Now this issue does repair itself by the next trip.
I am thinking the timing advance is affected in some way when the boat has the impact of the wave.
Looking at wiring i cant see anything that could short or have a momentary break that can cause it in the center console wher a boat wake would cause the most violent g force reaction.
Thanks for reading this loss post!

 

[Crosbyman]

but it did use up at least 3 gallons of gas in the mile.


OMG !!!! OMG-( check for leaks... lift pump rupture ...whatever ....

 

[airshot]

Had a similar issue on my 1979 70 ho Johnson OB. One time it would run perfect, then another time 1500 rpm was it ! Battled this for a month trying everything, even taking it to a mechanic. Of course it worked perfect every time for them. One day we went out together and it acted up, finally the mechanic took out a screw driver and whacked the CDI box and it took off !
Whacked it again and it stumbled back down to 1500 rpm...another whack and off it went running perfect. Now....don't go out and whack yours at my suggestion but it turned out to be a faulty CDI box. Probably a crack in the board that would open and close under heat, vibration or whatever....replaced that and we were good to go !!

 

[That old Mercury]

but it did use up at least 3 gallons of gas in the mile.


OMG !!!! OMG-( check for leaks... lift pump rupture ...whatever ....

Dont have any leaks, done the same thing last 3 times it done this after hitting a boat wake.
It does not like running full throttle at 9 mph!
One time it done it after hitting a boat wake maybe 5 miles from the ramp and i ran it any way and it burnt 8 gallons of gas from what it took to fill it up at the gas pump.
At that time i didnt care !
I went with go or blow ! I didnt care
Thanks

 

[That old Mercury]

Had a similar issue on my 1979 70 ho Johnson OB. One time it would run perfect, then another time 1500 rpm was it ! Battled this for a month trying everything, even taking it to a mechanic. Of course it worked perfect every time for them. One day we went out together and it acted up, finally the mechanic took out a screw driver and whacked the CDI box and it took off !
Whacked it again and it stumbled back down to 1500 rpm...another whack and off it went running perfect. Now....don't go out and whack yours at my suggestion but it turned out to be a faulty CDI box. Probably a crack in the board that would open and close under heat, vibration or whatever....replaced that and we were good to go !!

Even though the boat wake was like 1' tall when i hit it it was a light slap of course , but thats all it took.
It only happens Crossing a boat wake! No other time.
I am thinking it is CDI as well like a bad solder joint. It runs like it has lost high speed spark advance, like trigger signal??
I have a bunch of test equipment i take with me .
I am going to put my timing light in the boat also.
I have hit or kicked everything else so i dont have any problem whacking the CDI box ! LOL
I got a kicker to get me back to the ramp!
Thanks for that idea, It is Greatly Appreciated

 

[airshot]

That is what happened to mine, after a month if testing, checking everything and nothing showing up, the mechanic guy ask me about smacking the CDI before he did it ! What did I have to loose....go for it, had to try something!!
When he did, he wacked it a good one !! Funny part is it took off and when he wacked it again, it went back to limp mode. As he wacked it over and over again, it kept going back and forth between full run and limp mode !!
Guess we found it he says......

 

[That old Mercury]

That is what happened to mine, after a month if testing, checking everything and nothing showing up, the mechanic guy ask me about smacking the CDI before he did it ! What did I have to loose....go for it, had to try something!!
When he did, he wacked it a good one !! Funny part is it took off and when he wacked it again, it went back to limp mode. As he wacked it over and over again, it kept going back and forth between full run and limp mode !!
Guess we found it he says......

Hi airshot:
How were yall testing it?
Was it on the lake? On muffs?
In gear or out of gear?
The reason i am asking is when mine does this it will rev up fine in neutral but only bogs in gear.
But the it fixes itself so i have just been fishing in a less fished lake and avoiding boat wakes or i just come to a complete stop and i let the waves settle down.
Glad i dont saltwater fish any more because i would not be able to fish unless it was flat calm
Thanks for sharing your issues!

 

[matt167]

Hi airshot:
How were yall testing it?
Was it on the lake? On muffs?
In gear or out of gear?
The reason i am asking is when mine does this it will rev up fine in neutral but only bogs in gear.
But the it fixes itself so i have just been fishing in a less fished lake and avoiding boat wakes or i just come to a complete stop and i let the waves settle down.
Glad i dont saltwater fish any more because i would not be able to fish unless it was flat calm
Thanks for sharing your issues!

You won’t hear a failing ignition under a no load condition.

 

[saltchuckmatt]

Another guess, my first to me larger outboard was a 82 Johnson 90 HP. Bought it used from a dealer. Took it out and it seemed gutless on a 1971 18 ft Fiberform.

We were running around and all of the sudden it took off like a bat out of hell. Then dogged out. We decided to take it back to the dock and we ran out of gas. Drank 6 gallons in a very short time, to make a long story short got towed in by a sailboat of all things. A very embarrassing moment.

Dragged it back to the dealer and everybody himmed and hod for a while and then one mechanic said " remember we got that technical bulletin about loose main Jets"

He tightened up the main Jets and it worked perfect for 10 years. That motor even went in the drink and salt water and lasted another five. Very dependable motor even when it was trashed by its owner who was me.

If the power pack doesn't fix it try looking at the main Jets. Not sure you should be running it though the way it is, can't be good for it.

 

[That old Mercury]

Another guess, my first to me larger outboard was a 82 Johnson 90 HP. Bought it used from a dealer. Took it out and it seemed gutless on a 1971 18 ft Fiberform.

We were running around and all of the sudden it took off like a bat out of hell. Then dogged out. We decided to take it back to the dock and we ran out of gas. Drank 6 gallons in a very short time, to make a long story short got towed in by a sailboat of all things. A very embarrassing moment.

Dragged it back to the dealer and everybody himmed and hod for a while and then one mechanic said " remember we got that technical bulletin about loose main Jets"

He tightened up the main Jets and it worked perfect for 10 years. That motor even went in the drink and salt water and lasted another five. Very dependable motor even when it was trashed by its owner who was me.

If the power pack doesn't fix it try looking at the main Jets. Not sure you should be running it though the way it is, can't be good for it.

I have had the carbs off multiple times checking to see if a float was sticking causing it to run on only 2 cyclinders . I actually just polished the needle seats using valve lapping compound and a Qtip.
It actually improved the idle drasticly by removing the maching scratches from making the part.
Everything removable was tight and clean
Thanks

 

[That old Mercury]

Another guess, my first to me larger outboard was a 82 Johnson 90 HP. Bought it used from a dealer. Took it out and it seemed gutless on a 1971 18 ft Fiberform.

We were running around and all of the sudden it took off like a bat out of hell. Then dogged out. We decided to take it back to the dock and we ran out of gas. Drank 6 gallons in a very short time, to make a long story short got towed in by a sailboat of all things. A very embarrassing moment.

Dragged it back to the dealer and everybody himmed and hod for a while and then one mechanic said " remember we got that technical bulletin about loose main Jets"

He tightened up the main Jets and it worked perfect for 10 years. That motor even went in the drink and salt water and lasted another five. Very dependable motor even when it was trashed by its owner who was me.

If the power pack doesn't fix it try looking at the main Jets. Not sure you should be running it though the way it is, can't be good for it.

I havent ever been towed back yet
And this crazy boat motor bogging down when hitting a boat wake is why i bought a small kicker lol.
I know i shouldnt be running it , but if it blows up i will be rid of it ans start new with a 4 stroke.
Thanks for that info and i will check the jets again because i plan to pull the carbs and look at floats again.
I also plan to pull the sparks plugs anyway to see if any are wet and hopefully see which cyclinders have quit firing
Thanks

 

[That old Mercury]

You won’t hear a failing ignition under a no load condition.

So i guess i will tie it off to the dock or back it in the lake leaving it on the trailer and chock my jeep tires front and back and run it doing the tapping test.
I aint leaning out the back while someone drives it and start tapping on things, i be feel out !
Thanka

 

[airshot]

Hi airshot:
How were yall testing it?
Was it on the lake? On muffs?
In gear or out of gear?
The reason i am asking is when mine does this it will rev up fine in neutral but only bogs in gear.
But the it fixes itself so i have just been fishing in a less fished lake and avoiding boat wakes or i just come to a complete stop and i let the waves settle down.
Glad i dont saltwater fish any more because i would not be able to fish unless it was flat calm
Thanks for sharing your issues!

The mechanic had it in and out of his shop numerous times, and of course it never acted up for him. We finally decided to go together out on the water to try and get it to act up. The mechanic was very good to me, I know he had far mire hours in this than what he charged me for, but it had become a real pain in his @$$ so he was determined to fix it no matter what. Walking it was a last result as we were going to gamble and replace the CDI anyway.
Just got lucky UT happened when it did. The CDI box back then was around 300 bucks and he only added another 300 for labor. Not long after his shop was bought out by a larger marina and moved to a busier area and if course there prices sky rocketed up. Can't say this is your issue, but you need to try all the suggestions if your unsure.. Good Luck !!

 

[saltchuckmatt]

It's something out of the ordinary and don't fall into the 4 stroke lunacy....you will only have different problems.

 

[cyclops222]

Anybody else have a sinking float ? It would take 15 to 30 minutes to fully kill the motor. Some are really odd balls. Both Varnished cork floats. And the molded foam floats.
Fun days. Using the oars for over 1 hour.

Reminds me to check the oars & refinish them.

 

[That old Mercury]

It's something out of the ordinary and don't fall into the 4 stroke lunacy....you will only have different problems.

You are so true about that, i aint gave hope yet and i wont!
I will find the issue , i thive on a challange ! Thats when i do my best work.
Its just crazy that it runs so good until i hit a baby of a boat wake and it just dies.
Just to Hot to tinker with it right now. I will hopefully have it figured out by Monaday !

 

[That old Mercury]

Anybody else have a sinking float ? It would take 15 to 30 minutes to fully kill the motor. Some are really odd balls. Both Varnished cork floats. And the molded foam floats.
Fun days. Using the oars for over 1 hour.

Reminds me to check the oars & refinish them.

I have put in at least 5 different carb kits with floats.
Mine hits a boat wake and just stops going ! Dangest thing i ever saw in 30 years of boating

 

[racerone]

Well----All those carburetor kits makes it obvious that it is not a fuel issue.-----Take a close look at all wiring.----Run with a timing light to see if you can pinpoint a spark failure.

 

[saltchuckmatt]

Did you disconnect the kill wire? Maybe you did.

Jostling kill switch?

 

[That old Mercury]

Well----All those carburetor kits makes it obvious that it is not a fuel issue.-----Take a close look at all wiring.----Run with a timing light to see if you can pinpoint a spark failure.

The first few kits were the cheap ones , you know the ones where the float needle fitting doesnt match the threads in the carb!
I was just useing them to stop a flooding carb when i bought the boat so i could run it find all my problems and then order everything i needed .
It was NOT my best idea at the time.
I will be taking my timing light with me one my next trip.
Thanks for the input it is Greatly appreciated.