Johnson Takes off Suddenly

[AK4Dave]

I have a 1976, 55hp Johnson Seahorse. I will slowly and gradually increase the throttle and all seems well, but when acceleration gets to a certain point the rpms increase suddenly without any major change in the throttle. It's like it just jumps to full throttle from, say, medium throttle. I'm wondering if my timing/spark advance is off or it's the high speed needle adjustment.....or?
Thanks.....

 

[Chinewalker]

Re: Johnson Takes off Suddenly

Hello,
No high speed needle to adjust - it's fixed jets.
Take the cowling off and watch the linkage on the motor as you accelerate. It's possible something is sticking and then releasing rapidly.

 

[tashasdaddy]

Re: Johnson Takes off Suddenly

possible bad throttle cable.

 

[kenmyfam]

Re: Johnson Takes off Suddenly

Had a similar thing many years ago with a 60hp Evinrude. It was a bad coil kicking in and out. Just a thought though not an analysis.

 

[OptsyEagle]

Re: Johnson Takes off Suddenly

I would lean towards the coil as well. You should do a spark test to see how strong your coils are. When a cylinder kicks in and out the only thing you will notice is the gain and loss of power.

 

[AK4Dave]

Re: Johnson Takes off Suddenly

Yes, I also got to thinking maybe something was sticking as well but it's not noticeable. Yes, after I posted, I forgot that there is no adjustment in the high speed jet, I meant to say just a problem with the jet. Throttle seems to move freely, but I'll look close again.

Yesterday I bought a spark tester at Schucks, and was going to try and check the timing (ie Joe Reeves way), but after I got it home I noticed that this tester doesn't have a way to set the gap. Anyway....I guess it will still be ok to check the coil spark with it? It doesn't kick in and out....only in and a big gain in power. So could it be that it is only running on one cylinder at idle and then as I accelerate the coil kicks in the second cylinder? Should I check the coil spark like I would check the timing, ie, with the plugs out, or will it have to be running?
Thanks for all the help....

 

[jonesg]

Re: Johnson Takes off Suddenly

Another way to check is on the water where it happens ( at hi-rpm),
a timing light will allow you to run with all leads connected.
Better with 2 people.

You really need to get a gap tester for any meaningful spark test.
ground all the leads if you pull the plugs.

 

[OptsyEagle]

Re: Johnson Takes off Suddenly

The best way to check the spark is to take the spark plug boot off the plug and put it on the spark tester. The other end needs to be grounded. Set the gap for 7/16" and verify that you get a spark. If not, I like to reduce the gap a little to see if I even get a week spark. My suspicion is that you are probably intermittently going from a week to a stronger spark, which eventually allows that cylinder to fire. All you need to do this is place an aligator clip into the plug boot and figure out a way to hold it about 7/16" away from the powerhead. When you turn the flywheel, you should be able to see the spark jump from the clip to the powerhead. A darker room helps or just take a paper towel roll's cardboard core and place one end over the gap amd the other end over your eye, to block out the ambient light. If the spark is there you will see it. Keep all combustibles away and of course your eyes should be a least a foot away (if I even need to tell you that).

Another test to try is to just start it up and remove the boot of each cyclinder, one at a time, replacing the boot to the plug, before you remove the boot from the other plug. When you remove the plug boot the motor will either continue or it will stop. If the motor stops completely when you remove the boot of a plug, then you know the other cylinder was never firing (or it would have kept running). If nothing happens, then both cylinders were at least firing. Use some well insulated plyers to remove plug boots from running motors. The voltage on the good coil can shock you right through the insulator of the boot.

Good luck.

 

[AK4Dave]

Re: Johnson Takes off Suddenly

The best way to check the spark is to take the spark plug boot off the plug and put it on the spark tester. The other end needs to be grounded. Set the gap for 7/16" and verify that you get a spark. If not, I like to reduce the gap a little to see if I even get a week spark. My suspicion is that you are probably intermittently going from a week to a stronger spark, which eventually allows that cylinder to fire. All you need to do this is place an aligator clip into the plug boot and figure out a way to hold it about 7/16" away from the powerhead. When you turn the flywheel, you should be able to see the spark jump from the clip to the powerhead. A darker room helps or just take a paper towel roll's cardboard core and place one end over the gap amd the other end over your eye, to block out the ambient light. If the spark is there you will see it. Keep all combustibles away and of course your eyes should be a least a foot away (if I even need to tell you that).

Another test to try is to just start it up and remove the boot of each cyclinder, one at a time, replacing the boot to the plug, before you remove the boot from the other plug. When you remove the plug boot the motor will either continue or it will stop. If the motor stops completely when you remove the boot of a plug, then you know the other cylinder was never firing (or it would have kept running). If nothing happens, then both cylinders were at least firing. Use some well insulated plyers to remove plug boots from running motors. The voltage on the good coil can shock you right through the insulator of the boot.

Good luck.

Well I guess that was it. Fired it up, and when I pulled the #2 (bottom) boot nothing happened, and when I pulled the top it died. The spark tester seems to show very little light on either boots. Now I need to know.....(edit)....Well I was going to ask if an 1985 50hp Evinrude coil would be interchangeable, but I dug them out and I see they are entirely different, so I would guess not. Anyway, do you think that's it....just a bad coil? Should I check anything else? How much $ do they usually run and should I replace both on an engine this old? Thanks again for the help.

 

[OptsyEagle]

Re: Johnson Takes off Suddenly

It sure sounds like a coil failure to me but perhaps some others can chime in with their thoughts or other tests, before you buy one or two coils. It's also possible that you have dirty points but I put this one as less likely (not even sure if you model has points, but I suspect it has).

 

[jonesg]

Re: Johnson Takes off Suddenly

swap the coils around.

 

[AK4Dave]

Re: Johnson Takes off Suddenly

swap the coils around.

So then if I swap them around and it dies like before, only on the other cylinder this time, then this would pretty much mean a bad coil? How spendy are the coils?

 

[Chinewalker]

Re: Johnson Takes off Suddenly

Coils aren't too bad - they have them right here on iboats.

Also, your motor does not have points...

 

[jonesg]

Re: Johnson Takes off Suddenly

So then if I swap them around and it dies like before, only on the other cylinder this time, then this would pretty much mean a bad coil? How spendy are the coils?

correct, you are testing whether the problem ( no spark) follows the coil, if yes then obviously its the coil. They're relatively cheap.
But test your coil grounds before ordering, any corrosion will knock it out.
And try swapping plug wires if possible.

 

[ezeke]

Re: Johnson Takes off Suddenly

Test your propeller first, it may be spun.

 

[AK4Dave]

Re: Johnson Takes off Suddenly

correct, you are testing whether the problem ( no spark) follows the coil, if yes then obviously its the coil. They're relatively cheap.
But test your coil grounds before ordering, any corrosion will knock it out.
And try swapping plug wires if possible.

Ok, here's what happened..... I started the engine to get it warmed up. Then I moved the top plug wire to the bottom (because it would reach) and then used the ignition tester (as an extension) because the bottom plug wire wouldn't reach to the top. It wouldn't start. Switched them back to normal and it would start right away. Tried the switch around again, and still it wouldn't start. Tried this 4 times, wouldn't start with the wires switched. When cranking the engine, I seemed to notice that it almost sounded like it would backfire, or "pop", at almost the same amount of revolutions each time. So I take it this means there's something else going on other than a bad coil. Any ideas? Thanks....

 

[jonesg]

Re: Johnson Takes off Suddenly

Were it mine, I'd toss the coils and plug wires unless known to be newer than 30 yrs old.

if you lack the funds to do that then remove coils from engine, swap positions, clean the grounds and examine the back and bottoms of coils for cracks, if they're cracked just lose them.

just moving the plug wires doesn't help, then the engine is firing on the exhaust stroke, you need to physically move the coils. You might find just moving them and cleaning all contact surfaces does the trick too.

 

[F_R]

Re: Johnson Takes off Suddenly

Ok, here's what happened..... I started the engine to get it warmed up. Then I moved the top plug wire to the bottom (because it would reach) and then used the ignition tester (as an extension) because the bottom plug wire wouldn't reach to the top. It wouldn't start. Switched them back to normal and it would start right away. Tried the switch around again, and still it wouldn't start. Tried this 4 times, wouldn't start with the wires switched. When cranking the engine, I seemed to notice that it almost sounded like it would backfire, or "pop", at almost the same amount of revolutions each time. So I take it this means there's something else going on other than a bad coil. Any ideas? Thanks....

You simply cannot do that. Merely moving the wires to the opposite plugs makes it fire 180 degrees out of time. That is why it backfires. When the guys suggested swapping coils, they meant physically swapping the coils' positions, including the primary wires.

 

[AK4Dave]

Re: Johnson Takes off Suddenly

Well, I wondered about that, if I needed to actually switch around the coils, but not being that familiar with these things I thought I'd try doing what I did. Ok, I'll give er a go after work and let you know.
Thanks Again.....

 

[AK4Dave]

Re: Johnson Takes off Suddenly

Ok guys, I physically switched the coils around.....and the wires. It does the same thing, ie....start it up, pull the bottom plug wire....it keeps running, pull the top plug wire....it dies. Same as before I switched them. Now what?