Johnson Takes off Suddenly

[jbjennings]

Re: Johnson Takes off Suddenly

Sounds to me like you have a bad powerpack, if that motor has one. One side of the powerpack can send a signal, and the other not. Sounds like that is the case to me.
JMO,
JBJ

 

[AK4Dave]

Re: Johnson Takes off Suddenly

Sounds to me like you have a bad powerpack, if that motor has one. One side of the powerpack can send a signal, and the other not. Sounds like that is the case to me.
JMO,
JBJ

Yes, it has what they call a Power Pack 2. I have the service manual here, and it says how to check the power pack, but they call for a 3 position Neon test light with A/B Tap Load Buttons.....which I don't have. Is there any other way to test the power pack?
Thanks....

 

[jbjennings]

Re: Johnson Takes off Suddenly

Sorry Dave,
I'm almost positive you can, but I personally don't have the expertise to tell you how. You might be able to take it off and have someone test it for you. However, if some of the true outboard mechanics here advise you that is the problem, I'd trust their advice. With the symptoms you have, I feel confident that is the problem, but it is an expensive part so you definitely should get a 2nd and 3rd opinion.:redface:
Good luck,
JBJ

 

[ondarvr]

Re: Johnson Takes off Suddenly

This sounds more like a carb issue than an electrical problem, most electrical problems get worse as the RPMs increase, not better, that is unless there's a short in the spark advance linkage that may change with its position.

I would take the carb off the cylinder that?s not working at low speed and clean the low speed jets.

My 1975 had adjustment screws for low speed, not sure if the 76 does, but they should be on the front of the carb when the air box is removed, I think there were also holes in the air box to access the screws, just pop the plastic plugs out. Try closing it (count the turns) and then open more than it was and then back to where it was, do this while its running. Sometimes this will clean the passage if that's the problem.

It could also be the spark advance linkage sticking, or out of adjustment and suddenly advancing.

 

[AK4Dave]

Re: Johnson Takes off Suddenly

This sounds more like a carb issue than an electrical problem, most electrical problems get worse as the RPMs increase, not better, that is unless there's a short in the spark advance linkage that may change with its position.

I would take the carb off the cylinder that?s not working at low speed and clean the low speed jets.

My 1975 had adjustment screws for low speed, not sure if the 76 does, but they should be on the front of the carb when the air box is removed, I think there were also holes in the air box to access the screws, just pop the plastic plugs out. Try closing it (count the turns) and then open more than it was and then back to where it was, do this while its running. Sometimes this will clean the passage if that's the problem.

It could also be the spark advance linkage sticking, or out of adjustment and suddenly advancing.

Originally I believe I did have a carb problem because it wouldn't start, so the first thing I did was take both off, remove and inspect the hi and low speed jets, clean everything and put them back together. It had gunk in the bottom carb bowl. It started up then but wouldn't idle. I had to mess with the linkage to get it to idle without dieing. It seems though that it is idling a bit fast to stay running, which makes me wonder if it's only running on one cylinder at idle, and then kicks in for some reason when the rpms are up towards full throttle. Because of this sudden advance I was thinking it was out of tune and the spark advance was off. But most here seem to think it was a coil problem. Anyway, I guess Monday I could check in town and see if someone could test the power pack. Unless anybody has ideas on checking something else this weekend?

 

[jonesg]

Re: Johnson Takes off Suddenly

ok , lets fall back and regroup.

top cyl doesn't fire.
you then swapped coils and top cyl still doesn't fire.
therefore its not the coil because the problem doesn't follow the coil.

Not familiar with your 76 engine but you say it has a powerpack instead of points, well then you can either buy a powerpack or get a dva meter and test the PP. DVA meters are sold cheap on ebay. $60

But when I experienced the same symptoms on mine I got a new powerpack and that solved it. Got mine here on iBoats, sierra.
Its a bit of a gamble because it might not be the pack, so you decide, get the meter and test it or ...

 

[ondarvr]

Re: Johnson Takes off Suddenly

Without being able to inspect it in person it can be difficult to diagnose, but you gave us this information.

You said it was getting spark on both cylinders (although it looked weak).

There was junk in the carbs when you took them apart.

You had to mess with the linkage to get it to idle.

Runs well at high speed, but on only one cylinder at low RPMs.


Coils tend to fail at high RPM, but may work still work at low RPM (not the other way around), so a coil is not the likely cause and you proved it by switching them.

A power pack could cause this problem, but will cost $$ to replace and may not be the problem. The P/P on mine was replaced last year because after running for three hours it would lose power and not run at high speed, if it was shut off for a period of time it would work correctly again.

There are other bits of the electrical system that could cause this problem and they require test equipment, more $$.



Since there was junk in the carbs and it will cost no money to clean them again, or at least the bottom one. And from the info you've supplied a dirty or plugged low speed circuit could cause this type of problem, that's where I would look first.

 

[AK4Dave]

Re: Johnson Takes off Suddenly

Without being able to inspect it in person it can be difficult to diagnose, but you gave us this information.

You said it was getting spark on both cylinders (although it looked weak).

There was junk in the carbs when you took them apart.

You had to mess with the linkage to get it to idle.

Runs well at high speed, but on only one cylinder at low RPMs.


Coils tend to fail at high RPM, but may work still work at low RPM (not the other way around), so a coil is not the likely cause and you proved it by switching them.

A power pack could cause this problem, but will cost $$ to replace and may not be the problem. The P/P on mine was replaced last year because after running for three hours it would lose power and not run at high speed, if it was shut off for a period of time it would work correctly again.

There are other bits of the electrical system that could cause this problem and they require test equipment, more $$.


Since there was junk in the carbs and it will cost no money to clean them again, or at least the top one. And from the info you've supplied a dirty or plugged low speed circuit could cause this type of problem, that's where I would look first.

Thanks for your time guys.....I do appreciate it. Just wish we could figure out what the hell is wrong.........lol. Actually I do believe that it is only running on the top cylinder at low speed as when I pull that plug wire it dies. It still runs when I pull the bottom wire. Ok, I'll look at the bottom carb again and see what I can find.....
Thanks.

 

[AK4Dave]

Re: Johnson Takes off Suddenly

OK...........I didn't mess with the carb yet because I had a thought......(look out).....lol. I wondered that if I started it up, accelerated to the point where the rpms make the jump and held it there.....THEN unplugged the top plug wire, if it ran then the bottom cylinder must be firing. So I tried it. Kept the rpms up just above where it takes off and pulled the top plug wire. It still dies. I tried the same thing again but I pulled the bottom wire....there is a drop in rpms, but it still stays running. Souldn't it do the same when I pulled the top plug wire? So what then is this telling you guys? I have to work on the house today so can't tackle the carbs. So hope to hear what this latest info of mine might bring.....lol
Thanks...

 

[AK4Dave]

Re: Johnson Takes off Suddenly

OK...........I didn't mess with the carb yet because I had a thought......(look out).....lol. I wondered that if I started it up, accelerated to the point where the rpms make the jump and held it there.....THEN unplugged the top plug wire, if it ran then the bottom cylinder must be firing. So I tried it. Kept the rpms up just above where it takes off and pulled the top plug wire. It still dies. I tried the same thing again but I pulled the bottom wire....there is a drop in rpms, but it still stays running. Souldn't it do the same when I pulled the top plug wire? So what then is this telling you guys? I have to work on the house today so can't tackle the carbs. So hope to hear what this latest info of mine might bring.....lol
Thanks...

Any thoughts?

 

[ondarvr]

Re: Johnson Takes off Suddenly

Weak spark won't affect the power a great deal, meaning that if it "will" jump the gap, it "will" ignite the charge. A power pack can still mess with performance in this way though.

Check the compression on that cylinder and check the carb, both can limit the power output of a cylinder to the point where it won't run on that cylinder alone, but will add a slight amount of power to an already running engine. This is why when you pull the top plug it dies, but when you pull the bottom plug it just slows down.

Running it with a carb that is plugged and running lean can destroy that piston, check it now so if that?s the case you can prevent any damage, or further damage.