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Johnson 90 stalling at idle speed only when warm.

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Johnson 90 stalling at idle speed only when warm.

Old 06-03-2016, 12:24 PM
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Default Johnson 90 stalling at idle speed only when warm.

2001 Johnson 90 PLSIG. V4 Looper. Same as PLSID. No idea what the G is for.

Motor starts easily and will never stall at idle when cold. Will never stall on the hose(hot or cold).

I literally could launch the boat and idle in gear through a no wake zone for 20 miles without stalling.



Example of my problem:

I run 3 miles to the reef.

I turn the motor off while catching bait.

The longer the motor is off, the more likely the following happens(but it always happens to some degree):

Motor becomes more difficult to start(although always starts).

I always have to completely prime the fuel system in this situation. I can feel that there is no fuel(soft bulb) and I have to completely pump fuel from the tank to refill carbs/vapor separator. I can feel all the fuel that I am having to prime.

Once restarted, I usually get smoke(more smoke than a cold start) and have to advance the throttle in neutral until motor seems to "clear up" and have enough fuel.

If I accelerate slowly I quickly stall. Bumping the key will cause the motor to stall immediately.

If I attempt to "gun it" I stall immediately.

If i accelerate moderately, I will not stall, however it definitely is still "clearing up" for a few seconds while I come on plane and then it will run perfect at all speeds for the rest of the day. It will even be fine at trolling speed, provided I don't turn the motor off.

For example, I have never once stalled after a long run back to the ramp. I can wait in neutral for a ramp to open up, or I can idle around in gear indefinitely without stalling.

If I turned the engine off in the water at the ramp, I would have the same problems, although I have never felt the need to do it. I already know the result.


When I run the outboard on the hose, it idles at about 800 RPM after the quickstart feature disengages. This is probably low considering no back pressure correct?


In gear on the water, my idle is between 500 and 600 rpm in gear. This seems low.




Carbs are clean.
Plugs are new.
Compression has remained at 120 on all 4 for 2.5 years(3 tests).
No leaks from carbs(new bowls)
No leaks from vapor separator(new gasket)
Boat get used very frequently(always has fresh treated gas)
VRO is disabled and I premix 50/1
Tried 3 different primer bulbs.
Primer bulb is located vertically(arrow straight up) within a foot of the outboard.
New power pack.
Change fuel water separator filter every 3 months and analyze. Never had water or any contaminants.
Run Penzoil Semi Synthetic.
Motor runs flawlessly other than this.

I have taken off cowling and air silencer and squeezed bulb until rock hard. No leaks from the usual suspects. Primer bulb remains hard for an extended period of time.

The adjustable detent is set all the way to the + side.

Motor has done this from day one. There has been a random day or two when this problem didn't occur, but the problem is about as consistent as you can get.

I'm aware these old 2 strokes don't like trolling, but this seems to be something else.

Sorry for the long post. Just wanted to provide relevant info.

Thanks in advance for any help and suggestions.
Old 06-03-2016, 12:56 PM
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It could be as simple as increasing the idle rpm by advancing the initial timing. The throttle is closed at idle with all butterflies closed, the air bleeds set the fuel air ratio at idle. As those older motors wear sometimes the initial timing needs to be slightly advanced (1 or 2 degrees) to maintain idle due to back pressure when submerged in water.
Old 06-03-2016, 01:46 PM
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Did you "clean" the carbs? Is the throttle and timing set as per specs in the manual?
Old 06-03-2016, 02:05 PM
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Originally Posted by jayyy View Post
It could be as simple as increasing the idle rpm by advancing the initial timing. The throttle is closed at idle with all butterflies closed, the air bleeds set the fuel air ratio at idle. As those older motors wear sometimes the initial timing needs to be slightly advanced (1 or 2 degrees) to maintain idle due to back pressure when submerged in water.
Thanks for the quick reply.

Makes sense with regards to the idle rpm's on the muffs being low.

Maybe a stupid question but here goes.

Why am I needing to re-prime the system with what seems to be a relatively large amount of fuel after the outboard is turned off and at rest for a half an hour or so?

Carbs are presumably full when I turn off the motor? 30 minutes later I need to pump the bulb more than when I leave the boat untouched for a week.
Old 06-03-2016, 02:38 PM
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Have you checked the red primer handle to make sure it is fully clockwise . It sounds like an air leak somewhere in the line is allowing the fuel in the line to drain back to tank once you shut off , if you don't have an antisiphon fitting on tank. I see you have replaced gaskets on the engine fuel components. Look for any wet hose connections in there that could be allowing air back in. Have you replaced the gasket on fuel input strainer to the vapor separator nut?
Old 06-03-2016, 03:06 PM
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Originally Posted by Dacman View Post
Have you checked the red primer handle to make sure it is fully clockwise . It sounds like an air leak somewhere in the line is allowing the fuel in the line to drain back to tank once you shut off , if you don't have an antisiphon fitting on tank. I see you have replaced gaskets on the engine fuel components. Look for any wet hose connections in there that could be allowing air back in. Have you replaced the gasket on fuel input strainer to the vapor separator nut?
Yes, the primer solenoid handle is facing down.

I replaced the fuel filter within the year and replaced the o-ring. I remember because I ordered the filter online but not the o-ring. The local dealer got me for like $7 for the o-ring. LOL.

The old filter was like new, but I replaced anyway. I checked immediately for leaks and this is the first area I check for leaks now since it is directly where I am priming the fuel and easy to see.

I had fuel leaks when I first purchased the boat due to the warped carb bowls and a leaking vapor separator gasket that were replaced as soon as I purchased the boat. It got me in the habit of checking for leaks. Nothing is leaking under the cowling. I cleaned everything from the old leaks so any new leaks or even some residual dripping would be noticeable.

I am going to take a look at the anti siphon valve now.

Seems that the fuel is going somewhere and it is not leaking into the cowling.

Thanks again.



Edit:
I have installed 3 different primer bulbs within a foot of the outboard. They have all been installed vertically with the arrow pointed up obviously.

I just checked an old one by blowing through it in the direction of the arrow(fuel flow) and then sucking. The bulbs are working. Free flowing when blowing in the direction of the arrow and the valve functions and shuts when I for lack of a better term "suck on it" .

I will still check the anti-siphon tomorrow as this will be where I start(at the tank) checking every fuel line from the tank to the vapor separator.

Last edited by Cucumber; 06-03-2016 at 03:30 PM.
Old 06-03-2016, 04:24 PM
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Cut the fuel line off of the barb connector at tank so you will have a fresh hose connection to tighten down. If hose is brittle or hard I would replace it all the way to the engine. Unscrew the barbed fitting from the pickup fitting and check for corrosion on the barbs after the piece of hose is removed also checking inside the barbed fitting to see if it's an antisiphon or not. Check ball and spring or not. Most antisiphon barbed connectors are aluminum and corrosion on the barbs are a place for air leaks. If it is an ASV replace it with new .
Old 06-03-2016, 04:35 PM
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Will do.

All fuel lines from tank to vapor separator are less than a year old but..........

I am going to cut and re-clamp everything from the tank, fuel water separator, primer bulb,etc all the way to the vapor separator fuel filter just to be certain.

Then going to spend time on all fuel fittings,fuel lines, and clamps on the outboard.

Going to replace anti-siphon valve regardless as they are cheap.


Thanks again.
Old 06-03-2016, 04:43 PM
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I had similar issues on mine. It was so random it was hard to tell what fixed it.

I replaced tank pick up, put an asv in place of the shut off valve that was there, line from tank to engine, bulb and rebuilt the fuel pump over time.

The asv seemed to make mine worse so I got another shutoff valve. Johnson bulbs always seemed to work the best and last longer than any others.

Good luck.
Old 06-03-2016, 05:08 PM
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Great description of your problem sir! We are having the same issue with our Ocean Pro 225. We can leave the dock and idle under way, go up on plane, cruise around, back down to an idle cruise, and back to dock. Once at dock and while trying to trailer, it will cut out and won't start. Tries to but won't. Once back home, same symptoms on muffs until we push in key switch and prime it a little. It then starts, but sounds like it is barely running with a really low rpm until we advance the throttle just right and blow out the fuel or get enough fuel. We can't tell which one but we get that big puff of smoke. We also can't find a leak anywhere. We've made sure throttle plates are closed at idle, checked all fuel lines and fittings, changed water separator filter, primer bulb is vertical and acting normal. We're thinking of advancing the timing just a little to see if that helps.

Not trying to take over your thread but interested if you find a solution. If we do, we will gladly share it with you.

Thanks,

Caleb
Old 06-03-2016, 05:24 PM
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Hey guys, didnt have time to read the whole thread as Im about to head out, but when I first purchased my boat which came with a 70hp 3cyl Johnson, it displayed similar problems, however mine were as follows -

Running at cruise speed, then mooring at the beach
Hour or so later, come back to boat, start engine, never has issues starting, starts right up, but would sometimes stall whilst at idle (was a hit and miss thing).

After this occurred a few times, I always tried restarting the engine with the lever advanced (lifted up a little) to keep the RPM about 1,000-1,200rpm for about 10 or so seconds just after starting and after going back to idle it would be fine. Seemed to get the cob webs out (figure of speech), fuel fully primed and flowing, etc..

Do you vent your tanks? could be a pressure issue? if your primer bulb is firm, perhaps the internal tank pressure is flooding the carbs causing them to stall (air to fuel ratio)? or if its not firm, perhaps your carbs are leaking fuel back into the tank and taking in air at the same time? hence when you prime the bulb its feeling firm because its got trapped air? But when you start the engine, its not getting the correct amount of fuel, hence the hard starting.

Excess smoke would most likely be a result of over flooding the carbies.

Hope this helps and as I said, probably touched on parts already raised, if so, apologies.
Old 06-03-2016, 05:35 PM
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Originally Posted by calebollie View Post
Great description of your problem sir! We are having the same issue with our Ocean Pro 225. We can leave the dock and idle under way, go up on plane, cruise around, back down to an idle cruise, and back to dock. Once at dock and while trying to trailer, it will cut out and won't start. Tries to but won't. Once back home, same symptoms on muffs until we push in key switch and prime it a little. It then starts, but sounds like it is barely running with a really low rpm until we advance the throttle just right and blow out the fuel or get enough fuel. We can't tell which one but we get that big puff of smoke. We also can't find a leak anywhere. We've made sure throttle plates are closed at idle, checked all fuel lines and fittings, changed water separator filter, primer bulb is vertical and acting normal. We're thinking of advancing the timing just a little to see if that helps.

Not trying to take over your thread but interested if you find a solution. If we do, we will gladly share it with you.

Thanks,

Caleb
Thanks for your input!

Feel free to contribute anytime.

I've been following your thread as well.

Keep me posted on how advancing the timing helps. You and your father have done some great work so far and I know you will have that boat in excellent running condition sooner than later!

Thanks again Caleb.

I will update progress as it happens.
Old 06-03-2016, 05:45 PM
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Originally Posted by mcsd63 View Post
I had similar issues on mine. It was so random it was hard to tell what fixed it.

I replaced tank pick up, put an asv in place of the shut off valve that was there, line from tank to engine, bulb and rebuilt the fuel pump over time.

The asv seemed to make mine worse so I got another shutoff valve. Johnson bulbs always seemed to work the best and last longer than any others.

Good luck.
Thanks.

Going to try some easy(free) things first.

Things like fuel pump and pulse limiter have crossed my mind.

I'm thinking of checking the float in the vapor separator as well.

It's frustrating because there are tons of these threads on the web, but they either never get updated with the solution or they just kind of work themselves out like in your case.

It could be worse. At least it doesn't keep me off of the water and it hasn't gotten any worse over a couple years.

Thanks again.
Old 06-03-2016, 06:15 PM
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Originally Posted by Johnson70hp View Post

Running at cruise speed, then mooring at the beach
Hour or so later, come back to boat, start engine, never has issues starting, starts right up, but would sometimes stall whilst at idle (was a hit and miss thing).

After this occurred a few times, I always tried restarting the engine with the lever advanced (lifted up a little) to keep the RPM about 1,000-1,200rpm for about 10 or so seconds just after starting and after going back to idle it would be fine. Seemed to get the cob webs out (figure of speech), fuel fully primed and flowing, etc..


Do you vent your tanks? could be a pressure issue?

Hope this helps and as I said, probably touched on parts already raised, if so, apologies.

The part that I put in bold print is very familiar to me. Neutral throttle at 1200-1400 rpm to keep it running and then the rpms jump up after the "cob webs" go away. Throttle down, put it in gear and good to go.

About the vented tank. I recently replace the fuel fill line and the vent line.

I have no idea how my vent works. I understand how it works with regards to filling the tank, but I have seen many/most other boats with through hull style vents such as the one on the right.

http://www.thehulltruth.com/attachme...1&d=1465002455

They are always open/vented I assume.


http://www.thehulltruth.com/attachme...1&d=1465002455

Don't see how mine (on the left) would ever vent while the cap is screwed down tightly, you know, like anytime I am using the boat.

http://www.thehulltruth.com/attachme...1&d=1465002208

Thanks for the input.
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Old 06-03-2016, 08:00 PM
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There is a member here who goes by Seahorse he really knows OMC stuff, you might PM a request to him to chime in on this thread.
Old 06-03-2016, 08:06 PM
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My 115 Johnson had the same problem and it was the temp sensor. Unplug it and it'll run fine. It goes to your computer and the computer is sensing an overheat so it's shutting down the engine till it cools off. It will run wide open but not at idle just like you're saying
Old 06-03-2016, 08:18 PM
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Originally Posted by PRO-BLU View Post
My 115 Johnson had the same problem and it was the temp sensor. Unplug it and it'll run fine. It goes to your computer and the computer is sensing an overheat so it's shutting down the engine till it cools off. It will run wide open but not at idle just like you're saying

It's not going into safe mode.

If my engine overheats an alarm sounds and it goes into safe mode which limits my RPM's.

I kind of like that feature. Although I hope to never need it.



Not quite following your logic, but if I had a faulty temp sensor I would just replace it as opposed to disabling it.


I appreciate you taking the time to comment though. Thanks.
Old 06-03-2016, 08:31 PM
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My year 2000 Johnson 115 would act similarly. After rebuilding the carbs and rebuilding the gas portion of the OMS pump, the issue went away.
Old 06-03-2016, 11:20 PM
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Sounds like heat soak to me. I bet its fine if you have it off for 4 hours or more and prime before you start it?

That's how my 2000 150's were.

Probably wouldn't hurt to change all the fuel lines after the bulb if they have not been changed before, and check your diaphragm fuel pump.
Old 06-04-2016, 01:21 AM
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Originally Posted by Nomad15 View Post
Sounds like heat soak to me. I bet its fine if you have it off for 4 hours or more and prime before you start it?

4 hours definitely. Probably less than that.




That's how my 2000 150's were.

Probably wouldn't hurt to change all the fuel lines after the bulb if they have not been changed before, and check your diaphragm fuel pump.
That is the plan.

Thanks. Will research "heat soak"

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