1976 Johnson 25HP, misses, cuts out, neutrals out

Well, as this is my first post, i'll give some background information on myself.

I am have been an auto tech for a few years, however I have not worked around boat motors. I am a technical and qualified person to fix my own stuff, but I also enjoy learning new things. So if you dont think I will know something, please take the opportunity to teach me!

First off, its a 1976 Johnson 25HP, pull start, short shaft 2 stroke.

The boat starts great (1 or 2 pulls max). I had the carb rebuilt chasing this problem, without really doing any diagnostic work (has not had it done in quite some time, I figured it couldnt hurt). The Motor also runs well at WOT. However when you are idling to park at a dock or something the motor will cutt of. It will misfire once or twice, and shut off. It will do this any time I bring it down to a low idle, hot or cold.

The next problem is when I accelerate. If I am at a slow speed (4 MPH maybe) and give it full throttle, it will accelerate really roughly like it has a dead cyl or something (motor shakes back and fourth as it accelerates). However one at WOT everything seems to clear up, or if I back off the throttle (reduce the load) it will clear up.

In the automotive world this would indicate some sort of secondary ignition problem. However i dont know if this carries over to boat motor world. Another question I have is how many coils are on this boat motor? I have seen other threads that indicates a coil under the flywheel. However my motor has 2 coils right next to each spark plug. How do the 3 coils work on this system? Why 3? Or do I have a newer ignition system and no coil under the flywheel?

Also when I am turning the boat it neutrals out (revs high, motor seems to stop propelling the boat). I had always though this was due to some sort of cavitation near the prop, and it just hitting air in a turn, however is it possible that the actual cause is some sort of issue in the geartrain? If it is cavitation, how can I reduce it? Or is this some sort of issue with the lower unit? It only does it in a turn.

Thanks for any and all help you give,

-Pete

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

Are You sure is simply doesnt load up when iddling. Adjust low speed jet, this way: Turn the needle screw all the way in, and seat it GENTLY, too hard may damage seat and needle. Back it out 1 3/4 turn, as initial setting. Start and run boat at mid to WOT to warm it up and burn all excessive fuel in motor. Now go down to iddle, and leave in gear, motor pulling boat forward, unrestricted. Adjust iddle speed to the lowest, where it runs OK. Now start turning iddle mixture needle valve in, in 1/8 turns at a time, waiting for the motor to respond. If iddle speed starts to raise, adjust it down, if motor still runs without stalling. Proceed until motor starts to stall from lack of fuel. Back it out 1/8 from there. Test at running speed, and return to iddle. Repeat if needed. Adjust iddle speed to appropriate RPM. Now you should be able to leave it there for the rest of the season. Many times the problems you describe is the motor "4 stroking" from fuel it loads up when iddling, untill it is burned at speed.

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

G DANE,

Thanks for the response. This was my initial suspicion. I will go out on the lake and give it a try. I do remember seating, and backing off 1 3/4 turn or so, but I never tried messing with it on the lake. I did mess with the mixture screw though, and have it running pretty rich in order to keep it running well.

It is just strange that the motor runs exactly the same from before I rebuilt the carb to after I rebuilt the carb. But thats not to say its not the issue.

Did you have any advice on the neutraling out problem i'm having? Or does it just sound like the prop is hitting cavitation. I dont hear any loud grinding noises or anything like that. If it is just cavitation how do I correct for it? I have a hydrofoil on the motor, I dont know if this makes any difference at all.

Again thanks for your help.

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

Hi again. The neutralling out is most likely ventilation, air pulled in from side when turning. Maybe motor ought to sit a tad lower on transom. When prop looses grip it will not get it back before you back off on throttle.

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

As for the slipping, look at the prop 1st. Could be a spun rubber hub in the prop or as in a case I experienced, the engine ran fine but under acceleration it would slip badly. I later found out that even though the prop looked in good shape it had actually been reworked 3 different times and was now over an inch in diameter smaller that it was supposed to be. A different prop instantly fixed the proplem.

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

Ok everyone, here I am again and I REALLY need help with this thing.

None of the problems have changed since last season.

Over the winter I tore the engine down and inspected. The pistons and cylinder walls look great. (compression was 90 psi in 1 pull, 110 on second pull, then 120 on 3rd pull for both cylinders).

I inspected the reed valves and verified that they are in good shape.

One question on them though, I noticed that I can see some light between the valve and the plate when I have it off. Big deal? (very small gap)

The carb has been rebuilt again, this time I removed all of the plugs and everything, cleaned with compressed air and replaced everything.

New points/condensor (set to .020), new driver coil (under flywheel) new coils on side of motor (old ones had huge cracks in them).

Replaced upper and lower crank seals.

Retested for vacuum leaks using brake cleaner (none found)

Set the throttle roller between the 2 marks on the cam, and set the throttle blade to just start to open.

Rebuilt fuel pump, replaced all fuel lines

I am at a total loss. There is no reason this motor should be running poorly.

To restate my problem:

Motor misfires when I attempt to take off under load. I can rev it with no load and it runs just fine. It will only misfire after I have been Idling it (like it is loading up on gas). Then if I give it mid to full throttle it misses. After a few seconds the misfire will clear up. I can then go all the way back to idle and full throttle with no problem. But if I run around at low speed for about 10 seconds and give it mid-full throttle the misfire comes back.

To me it seems like the lower cylinder is loading up on gas. If I try to adjust the low speed mix screw any leaner it will pop and the engine will die. right now it is set to 1-1.5 turns out.

I just cant figure this thing out...Ready to unscrew the mounts and throw it into the lake...

I was also reading that a bad clutch dog can exhibit symptoms of a misfire under load.

That is another problem, every once in while if I give the motor mid to full throttle it will just rev up and not go anywhere.

I can give it a little throttle and the boat will start to move, but if I crack it open quickly it will rev up and unload until I bring it back to idle speed and then something will kick back into gear.

I have had the lower unit apart and I dont see any evidence of wear. No metal shavings or anything. The clutch dog physically looked ok. When it was acting up I grabbed the shift lever to verify it wasnt kicking out of gear.

Im at a loss. Any help would be appreciated. I have gone through everything on this motor...

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

just to be sure, you're running 50:1?

My 25's behave as you describe until I run a can of fuel through each season.
I'm on the rich/lean knob a lot the first outing. They have a low-mid hesitation where they sound like they are getting flooded.
The cure is a good long run at mid and wot.
I find I replace plugs in these 22 CID motors a lot compared to other motors. (twice a season minimum) gap at .030"
I forget which plug I have in there now... I may have switched from the J4J originals. J6C maybe? or maybe an NGK B6S - I'll check

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

Just some of my thoughts.....

Make a mark across the prop hub and see if the mark moves to verify that the hub is not bad in the prop, causing it to slip under power and let the motor overrev.
If it feels like you hit something just before it loses power, it's probably a bad shifter adjustment, or clutch dog.

As to the running problem, all I can guess is possibly a vaccuum leak, misadjusted float, pinhole leak in the fuel pump diaphram, or a bad lower crank seal. One question, what does it do when you adjust the idle needle clockwise a little at a time? Does the motor start to idle higher, and then start coughing and die unless you back off of it? If not, there may be something wrong in the idle circuit. You can check for vacuum leaks by spraying propane (with an unlit propane torch) around the intake to carb mounts, fuel line connctions, etc.; or, even probably by spraying some wd-40 around it as well.
Sounds like a hard problem to identify.
GOod luck,
JBJ

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

How about the armature plate is it moving? if it is that can cause some likly problems.Have you put a timing light on it? does the timing mark jump around? That could mean the armature plate is moving.
The reving when gassing it sounds like a spun prop like a poster before mentions

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

I did put a mark on the prop and it did not appear to move. Unless it just spun and happened to stop in the same spot.

The upper and lower crank seals have been replaced

I'm running 50:1 mix

The spark plugs are new. I put in J8C as recommended by a local marine tech.

If I do run it at WOT for a while I can bring it down to idle and accelerate right away without a problem. If I stay at idle for a few seconds it will mis under acceleration.

The fuel pump has been rebuilt, I even took it off and verified last night by removing the intake transfer port cover and bolting it to the fuel pump, then pumping the primer bulb and pulling a vacuum on the backside of the pump. It didn't even get slightly wet.

I did spray brake cleaner everywhere and noticed no change in RPM.

I had the carb apart the other day and rebuilt it again for fun, and ensured the float is sitting level when the carb is upside down, and when it is right side up the float hangs down 3/4 of an inch as per the instructions on the book.

When I turn the idle screw in the motor will idle higher, and will start to pop and die.

I can get it set so the motor will idle good, then when I give it gas it sounds like it is running on 1 cylinder. After a run at WOT and I bring it back down it will idle like crap again for a while. As in I cannot bring the throttle back down to slow speed, I have to very gradually bring it to mid, then a little less, then a little less, until I finally hit the slowest it will go. That whole process would take like 2 min to get it to idle smoothly again.

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

J8C's are too hot imo, but I'm going to check what I have in mine before I suggest that's the whole problem

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

O.k.,
Then I have one last suggestion. It sounds like there is some kind of fuel restriction preventing the fuel bowl from staying filled. I wonder if it's possible you have a clogged fuel filter, or possibly a split in the pickup tube in the tank letting it suck air, or a tank vent that's not letting air in the tank. You might try squeezing the primer bulb and seeing what happens while it's running (if you haven't already).
That's about all I can think of, unless you have intermittent spark on one coil or a wire that's arcing when the armature is in a certain position.
I hope you find the booger,
JBJ

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

just did some googling- guys like Joe Reeves and other OMC techs seem to say frequently that J8C's are piston melters in J/E twins and nothing hotter than J6C should be used.
J4C's for a lot of WOT running
J6C's for a lot of trolling and in high hour engines.

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

I have J4C's in mine.

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

Just a thought, run it at idle until it stalls on you, pull the lower plug and check it. Is it fouled with fuel mixture? If so, you fuel pump is leaking through the diaphram. The fuel pump is plused by the lower cylinder, a leak there will flood the cylinder but it will clean itself out at high speed.

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

Ok, i'll try the J6C's.

Just looking over everything it is all in perfect shape. I did a static check on timing.

One cylinder is outside of the window by 1/4" advanced (to the right) the other falls right on the end of the retarted side range (to the left). I'll have to get it back in the test tank to check it dynamically. Otherwise I'll re time it and see where that gets me.

Thanks for the help so far I appreciate everyones suggestions, even if I have already done it 3 times I'll gladly do it again to ensure it was done correctly.

Please let me know if anyone has any other thoughts.

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

this thread is saved in my "weird and cool" folder -interesting read:
http://forums.iboats.com/showthread.php?t=279981

Re: 1976 Johnson 25HP, misses, cuts out, neutrals out

Holy Mother of ......

I was just coming on here to ask if it was possible for my flywheel magnets to be getting weak.

Today I retimed the engine and ran it, I noticed that I still had some issues, however I was able to get them to clear up a little bit by reducing the spark plug gap to .025". The larger the gap the larger the resistance therefore more power would be needed to jump it. If my magnets are getting weak there would be less power induced into the driver coil, and a weaker spark.

I did install a replacement driver coil, now I think I will dig my old one out of the garbage and run it in parallel to see what happens.

Thank you so much for the info I hope it works.

It was almost scary reading that post because it was confirming my thoughts about the flywheel magnets....

Man it is 1:00am here and all I want to do is go install that thing now...