87 Johnson 50 HP, Wandering Idle - STUMPED

Frizzlestick

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I have an 87 Johnson, 50 HP. It was VRO, but that unit failed a few years back - so now I just mix 50:1 right at the tank.

The problem is a wandering idle of sorts. At certain RPMs, most notably at idle, it wanders. Like it's rough, then good, then rough, then good. At full throttle, and other points in the throttle, it's fine. At others, it has this wander about it.

Things I've checked:

  • Compression : good in both cylinders - one was 133 PSI, the other was 139 PSI.
  • Manual Choke/Primer Switch: In the right position and works correctly.
  • Spark : The coils seem to be producing good spark, put a tester on both wires and they were arcing/lighting up fine (one better than the other, but the weaker one is still well in the acceptable range.
  • Carbs: I had a mechanic do a rebuild on the carbs. New floats, needles, gaskets. They looked in good shape anyhow, but did it "just in case". They're fixed, so I can't adjust the mixture. Jets were clean.
  • Fuel: Fresh fuel, 50:1. Ran Seafoam through one tank. New fuel lines from tank to motor, including primer bulb.
  • Plugs: The plugs seem to be fine. They're a bit wetter than I expected, but not "jeez, this ain't burning nuttin'" wet. Pulling them and cleaning them has no noticeable effect.


I've run some sea-foam through the tank, and put some deep creep right into the throttle/carbs under load (to try and clean out the reeds), no change. I've also replaced the fuel line with no change.

Now the only thing that makes me scratch my head, is that if I shoot carb-cleaner in it when it's running, it runs well while I am shooting it, then once that burns through, it's right back to wandering. That has me scratching my head because I would think it's running lean/starved, and the carb cleaner is helping it - but with the plugs being wet(ish, not terribly bad or ineffective) makes me think it's rich(ish).

I would also think, that if it was the reed valves (gummed or cracked), that carb cleaner wouldn't have any temporarily improving effect on it?

Also, would like to add that sometimes, rarely, it's fine. Idles like a dream, motors about like a dream. But most of the time (90%?) it's wandering idle and this surging/wandering at certain RPMs (with full throttle being fine, and about half-ish throttle, and somewhere just above idle -- i can usually find a spot where it evens out in the firing).

Ideas? I'm scratching my head here. Plugs say "maybe a bit too wet", carb cleaner kinda tells me "maybe a bit too lean", loping tells me "maybe bad plug/spark/air in the line?"
 

Frizzlestick

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

I should add that the motor seems to start fine (with the primer), its just that rough/wandering idle - the one that stumps me is that with a shot of carb cleaner, it smooths out.

I suspect it's running a bit more rich than it should be, since if I wait five minutes and try to start it, it wants to be primer'd again.
 

Frizzlestick

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

I guess if I had to say, I'd say it's running rich, most/some of the time. The exhaust has more blue smoke than I'm used to, and at certain speeds the exhaust is giving up smokey bubbles in the water (exhaust from propeller). Compression is fine, though.

I wonder if maybe it's the leaf/reeds? Would that cause a wandering/loping/rough idle and rich condition? Something that seems to be fine at certain RPMs? Also with shooting carb cleaner it levels out (RPMs increase a bit, but is smoother?)

Ideas? Anyone?
 

Watermann

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

Do you have a tach to see if the rpms are jumping up and down when at an idle? Spray the carb cleaner around the outside of the carbs rather than inside the throat and see if the idle picks up. I wonder if there's a vacuum leak like maybe a gasket got put on out of whack. As far as spraying the cleaner in the throat picking up the idle, that's what happens when the motor gets more fuel which causes the rpms to increase to hit the sweet spot where it doesn't "wander". Maybe the guy didn't do such a great job rebuilding the carbs and missed something? I know it's nice to have everything perfect but actually how often do you just sit and let your motor idle to be annoyed by it?
 

Frizzlestick

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

Watermann, thanks for the reply.

It's definitely wandering RPMs, it's almost as if someone chooses to lightly rev it a bit. I keep thinking I should post a youtube video of what it's doing so folks can hear what I'm trying to describe. It'll low idle put put put put and then up the RPMs an then back down again. Like it's bogging and then getting right and then bogging.

It's not just at idle that it does this surging/hunting/wandering. It does it at other RPMs, also. I can generally find sweet spots in the throttle where it doesn't do it (and let it run there when I'm using it). Notably full throttle, somewhere at half throttle, and also a bit above idle and about 1/4 throttle. It seems I can find spots in the throttle where it smooths out. It's also running richer, I've noticed that, too (which is why I was fearing/thinking the reed/leaves).

I can try and zap some carb cleaner outside the body instead of inside the throats. It at least gives me something to try.
 

Watermann

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

Hey a video would be very helpful. It does sound like a fuel delivery problem to me.
 

TrueNorthist

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

I would also suggest you stop spraying carb cleaner into the cylinders. The stuff doesn't do much when used that way and will in fact cause damage with excessive use. Did the mechanic install the carbs, or did you do that yourself?
 

Frizzlestick

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

The mechanic installed the carbs and did the carb rebuild (which was our first guess, but the carbs were clean).

I'm currently uploading two Youtube videos. One shows the extreme (where it picks up RPMs, farts a little blue and then settles back down). The other demonstrates me spraying down on some fuel lines near the fuel filter and it picking up RPMs (I say "spraying" and give it a shot). The audio seems a bit tinny and doesn't demonstrate how extreme it can go.

1. Wandering Idle: Wandering idle - YouTube
With this, at 0:10, you can hear it wander up a bit then settle down again, twice. That's not messing with throttle, that's what it just does, at random times.

2. Spray Increases RPMs: Spray ups RPMs - YouTube
You can hear it loping a little before I spray it. This one shows that when I spray down around the fuel filter (its new, connections too), RPMs go up. I did this a few times to verify. It finally stopped after soaking the area from so many sprays. :)

Since, I replaced the plugs (just in case) and it was better, but not gone. I took some carb-cleaner and shot it around the gaskets of the intake manifold, where the gaskets all are, and got no results - so no leak in the gaskets around there (it was a pain, because the spray would atomize in the wind, get sucked in to the silencer and fool me, I had to make a snorkel of sorts for the silencer).

Then I moved to shooting the fuel line in different areas from the tank down to right into the carbs. At this point, I'm beginning to think that it might be a bad fuel line somewhere on the side. A dry/cracked hose somewhere. When I'd shoot around the filter (it's new), it'd cause the RPMs to increase. I think it might be the hose buried underneath the filter. After some liberal spraying around, it stopped being so extreme and got better (I could take it on the lake and idle smooth at 3 MPH), and the top-end was smooth (at around 20MPH). I am suspecting the spraying of a dry/cracked hose line wetted/softened it, and the dry crack isn't as pronounced anymore.

Better, but not gone. More ranges in the throttle were "normal" but some were still loping/wandering/surging. It does this surging/loping at all ranges of load and throttle. There are some sweet spots in the throttle where it goes away, but it's across the whole range of throttle it can behave like this.

I'll probably replace the fuel lines tomorrow, just cuz. Not sure what else could be causing the random increase in RPMs (and apparent increase in richness, based on the puffs coming out after an RPM wander up).
 

TrueNorthist

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

I think you have an intake leak. That is why it revs up when you spray in there. It looks like it also got very hot at some point so it could be cracked or warped, but I'd check the carb gaskets and reed block. If somebody did the work you should take it back to whoever did it.
 

Frizzlestick

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

I think you have an intake leak. That is why it revs up when you spray in there. It looks like it also got very hot at some point so it could be cracked or warped, but I'd check the carb gaskets and reed block. If somebody did the work you should take it back to whoever did it.

How does it look like it got very hot? I'm not seeing that indication? The compression is strong and not a big variant between the two.

When I spray the intake manifold, or that reed/leaf manifold bolted on to it (where the carbs bolt onto) - I don't get the revving, I checked those thoroughly. I only get the revving when i shoot the hose lines at/underneath the fuel filter area.

Is it possible it's just the leaves/reeds themselves?
 

TrueNorthist

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

The powerhead paint is missing and what is there is really dark. Often indicates heat, but it might just be rust... I am thinking an intake leak because spraying the fuel line would not affect the idle so quickly. It acts like it has a leak somewhere close to that area.
 

Frizzlestick

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

The powerhead has good black paint, just under a bunch of grime. I get what you're saying about immediate response, but it does do that too if i zap right into the silencer. I tried being very thorough about isolating the parts i was spraying. I shot the manifold behind it specifically after the hose test and got no response. I can look closer when i swap out the fuel lines tomorrow.
 

Watermann

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

Did you take the carbs to the guy to have them rebuilt or the entire motor for the job? Most marine mechanics I know replace all of the fuel lines under the cowel when doing a carb rebuild and put new zip ties on them nice and tight.
 

brnschoneck

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

how about fuel pumps mine was doing same thing last week i did carbs , primer buld , fuel pumps, timing and its good to go purred like a kitten this am ...I am going to a mech.. tommarrow just to do some finall adjustments ...Also make sure you fuel tank is vented properly the screw can vibrate closed and itll do this ????
 

waterman556

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Re: 87 Johnson 50 HP, Wandering Idle - STUMPED

Have you hit a stump or dragged the prop in the mud ? If you have you may have nicked your flywheel key.I had that happen to me on my 70hp rude.Just a thought.
 
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