1977 Johnson 6hp, is my diagnosis correct?

BoatThings

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Got a sudden loss of power accompanied by a nasty racket out on the water. Immediately checked the pee stream, good flow and temp was fine, killed the engine, checked around inside the cover, no overheating. Was out camping in the canoe, and on the way back to the vehicle. Still pretty far out, so I figured I try to start it again. Harder to start than usual but came back to life and ran fine for another 20 minutes or so, then did the same thing.

Got it home now and pulled the plugs to check compression, found the bottom plug completely wet with fuel, (might be hard to see in the pics, but the fuel is actually bridging the electrodes) first instinct is that it's running one one cylinder from an ignition problem. Check compression to make sure it's not the head gasket, or something worse. Got 60 on top, which is normal when it's dry, and 90 on the bottom, which is normal when it's wet, which the bottom was, quite wet, while the top was dry. I still see spark on both plugs out of the cylinders, and when I put them back in to check under compression with an inline spark test light, they also both work. Upon checking the ignition coils, I found the primaries good, but both secondaries are out, the bottom around 1300 ohm and the top is around 1500 ohm, when I believe they are supposed to be 275 +/- 50 ohms.

Seems to me I have some weak coils, visual inspection also shows a crack on the plastic covering of the top coil, and even though it's more out of spec, it seems to be the bottom one cutting out, possibly from heat expansion.

Even if the problem lies elsewhere, looks like I'm in need of some new coils, but I have no experience with small two stroke marine engines, this is my first, so I thought I'd bounce this around to get any other possible ideas to make sure I'm on the right track.

On a side note, all of my attempted restarts also broke my pull rope, so I replaced that, and then discovered my pinion gear was cracked at the top, so I 3D printed a reinforcing collar and epoxied it back together. Might also be running a little rich in general, but these plugs are 3 years old, I probably only use the motor for less than 10 hours per year.
 

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F_R

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You sure that Is fuel and not water on the plug?
 

jimmbo

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60 psi on top and 90 on bottom, somehow doesn't sound kosher to me. Pull the head, you might just have a less than perfect gasket, or a slightly warped head. Also remove the transfer port cover and look at the piston skirts, and check the rings for tension
 

racerone

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Are there transfer port covers on a 6 HP model ???----I don't think so !
 

BoatThings

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If I squirt some fuel/oil into the top cylinder it gets to 90psi too, it's just the better seal from it being "wet" with fuel and gas. And yes, it was absolutely 50:1 fuel/oil mix on the plug, not water.

Both cylinders have the same compression if they are both wet or both dry, let's not fixate on that. If the head gasket was a problem on the non-firing cylinder I would see a big drop on that one, not a higher reading (from it being soaked with fuel and oil creating a better seal than the top dry cylinder). At least that's what would make sense to me.

I'm still convinced it just bad ignition on that bottom cylinder, but definitely welcome to other ideas I haven't thought of. What else could cause a fuel flooded non-firing bottom cylinder that still has good compression?
 
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jimmbo

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Check compression to make sure it's not the head gasket, or something worse. Got 60 on top, which is normal when it's dry, and 90 on the bottom, which is normal when it's wet, .

That doesn't sound right.
 

BoatThings

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Wishing I didn't mention the compression readings now, just a distraction. I compression check my engine every year, I'm familiar with how it works. Go try the compression on an old two stroke dry, then wet the cylinder with fuel and oil and check it again, and then tell me it doesn't sound right? Let's forget about this avenue for now, I'm 99% confident it's not part of the issue, especially since the high compression is on the flooded non-running cylinder. I already mentioned that when I wet the top cylinder, it also goes to 90psi, the oil makes a better seal around the rings, especially in an older, sloppy, cold two-stroke. I merely mentioned it to showcase further that the lower cylinder was flooded. Nothing wrong with 60-90 psi on these old OMCs, as long as it's even, which it is, when both cylinders are either dry or wet. I would hope anyone commenting about the compression not sounding right would have some actual experience with exactly what I just mentioned turning out differently that they could talk about, or you're really just muddying the waters here.

I have already confirmed that the coils are way out of spec, 1300-1500 ohm instead of 275, so quite likely the problem, but not definitely.

I'll check the fuel pump diaphragm, but would it be likely for only one cylinder to be flooded by such a failure? I also don't think this would be an intermittent failure, which ignition can be, as I did get going again normally for a while before the bottom cylinder crapped out again.
 

racerone

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I believe you will be able to sort this simple motor out yourself.-----The nasty racket would be a huge concern to me.-----Should be easy to determine what went wrong.------Good luck with the trouble shooting !
 

Crosbyman

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surprising that both coils are way above 275 ohms…at the same time

did you test with coils mounted or off the motor

if you measured on the engine… remove them and polish all connection junctures to ensure proper grounding and continuity measurements
 

BoatThings

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Thanks Racerone, I hope your'e right!

Coils were mounted when I tested them, but I grounded right to the ring terminal of the coil, and cleaned it up a bit before doing so. I will definitely follow your advice though, as it does seem odd. I used a couple different meters to confirm my readings for this reason as well.
 

racerone

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Easy to overhaul one of those motors.---No manual needed on my workbench.
 

BoatThings

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Nice crack on the case of both coils. Still testing high, but nearly identical now. I discovered that the boot on the top coil is temperamental, got no continuity at all until pushing on the boot a certain way, and then got it to read ~1300 instead of the ~1500 I got before. I may have been the final cause of this break though, through my fiddling.

If this is just the way these coils life out, that evenly, I'm impressed. Also still just on the edge of working this far out of spec. I'm still a littler perplexed as to how the top coil seems to be worse, but the bottom cylinder stopped firing. Still entirely possible though, that with some heat expansion after running the motor a while, that the bottom coil develops an open circuit somewhere.

I also checked the sensor coil, 40 ohms +/- 10, and got 38, as well as the charge coil, 575 ohms +/- 75, and got 562, so all good there.

Now to source some coils. I seem to be finding two different part numbers. 581670 and 584561. Not quite sure what's going on yet, but still looking into it. Also planning to open up the coils. Interested to see where the extra resistance is. If it's just in the high tension leads, I may try to replace just those, if I can find similar resistance wire, to keep as spares. This incident has made me realize that I should definitely do some more thorough checks and get some spare parts in order! I get pretty far out there sometimes, always well equipped, but would still not be fun getting left with a long paddle and a heavily loaded boat.
 

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Tim Frank

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How are you so sure that it is not water on the plug? ...or a 50:1:20 mix of fuel and water?

Can the ignition spark across a 7/16" open air gap? Those in-line testers are iffy in my experience....and testing with the plug grounded to the block only tells you that you have spark with the plugs grounded on the block....and it won't run that way. :)
Make sure the HT leads are solid-wire core.

You said in post 1 that you have no experience with small two cycle motors and then seem happy to dust off advice from some of the gurus....probably not the optimum course. :)

Nothing wrong with 60-90 psi on these old OMCs, as long as it's even, which it is, when both cylinders are either dry or wet. I would hope anyone commenting about the compression not sounding right would have some actual experience with exactly what I just mentioned turning out differently that they could talk about, or you're really just muddying the waters here.

Not to muddy the waters, but after 40+ years of working on these, selective "wet or dry" compression testing is a mug's game. There are a number of significant faults that could be showing from those compression readings.
A "nasty racket" would have me finding the source....not breaking the pull cord trying to restart.

But that is just me.
 

Crosbyman

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still curious about those high resistance values…. maybe the end connectors are oxydized…

do an autopsy… open a booth end and look see
 

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BoatThings

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Hey Frank, I figured some old "guru" would try to dress me down at some point. Thanks for the "help"!

The racket was likely the noise of running on a single cylinder, but I'll confirm that when I get things going again. I already explained that I was hours out when it happened, or I wouldn't have tried to restart the engine. While we're taking shots at each other, I might suggest brushing up on your reading comprehension.

How am I so sure it was fuel on the plug? I could see the blue tint of two stroke oil, clear, no emulsion, I tapped it onto a sheet of glass, and lit it on fire. Also very obvious from looking into the cylinder through the spark plug hole.

I also mention that wetting the top cylinder brings it to 90PSI, same as the bottom. This is not selective testing, the bottom just happened to be wet from flooding, and I know from experience with my motor what it reads when wet or dry. Does your experience really lead you to see a problem with this? I think it's much more likely that it's your ego with the problem, but if you have some actual technical experience with this situation, instead of a personal attack, please share.

Pretty curious how none of the "gurus" are interested in the 1300ohm ignition coils, and seem to just want to take shots at me.. telling.
 
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BoatThings

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Crosyman, thanks for your interest in the actual problem here, and not your own ego, it's much appreciated.

I'll definitely do an autopsy, I'm curious as well. Just took a quick look at the connectors and they're a little tough to see, but appear to be ok.
 

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iggyw1

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Oops! I would venture to say that you got all the help that you're going to get from the gurus, "the guys that would help you the most" because of the "thanks" that you gave them with your attitude. I do not think that they were taking any shots at you. They were simply trying to help you until you blew it!! Every time I asked for help, I listened to them and they were ALWAYS right on the money.
 

BoatThings

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iggy -"ALWAYS right on the money."

Example of "guru" "help" received:

Jimmbo - "60 psi on top and 90 on bottom, somehow doesn't sound kosher to me. Pull the head, you might just have a less than perfect gasket, or a slightly warped head. Also remove the transfer port cover and look at the piston skirts, and check the rings for tension"

racerone - "Are there transfer port covers on a 6 HP model ???----I don't think so !"

If you're initial response is that you want to scold me, and have no interest or knowledge to offer about the 1300 ohm coils that should be 275 +/- 50, that's not being a "guru", that's being childish.

Can we move on to the actual technical problem here? Check the ego before posting.
 
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