Johnson 70 firing on 2 of 3

[clintcela]

Hello all,

I have a J70ELCRD, or 1984 Johnson 70 ouboard.
I just bought the boat and already

• 
  changed the impeller
  changed lower unit gear oil
  new spark plugs (gapped at 0.40)
  rebuilt and cleaned carbs with kit including new floats
  changed gas lines from in-floor tank all the way to the motor
  replaced squeeze ball pump and inline filter

My problem is that it is not firing on the top cylinder.
I pulled the spark plug wires one at a time while idling on muffs.
Pulling 1 is no change.
Pulling 2 or 3 and it runs rough then stalls.
I got the high voltage jolt when taking the wire off #1.
Plus I swapped the coils with #2 just to check and no change.

Compression tested at 120, 121 and 119 respectively top to bottom.

What could it be?

 

[Lyle29464]

Re: Johnson 70 firing on 2 of 3

Try a little gas in the top carb.

 

[Will Bark]

Re: Johnson 70 firing on 2 of 3

Gap plugs at .30 and check all with an in-line spark tester. Is #1 wet or dry when you pulled the plug?

 

[clintcela]

Re: Johnson 70 firing on 2 of 3

Thanks for the advice.

I gapped to 0.30, put gas in the carb manually, cranked right up but still only running on bottom 2.
Pulled the plug and it is wet so that shows the gas is getting in the chamber, correct?

And measured spark gap at almost 3/4 inch.

Still same problem.
Any ideas?

 

[Will Bark]

Re: Johnson 70 firing on 2 of 3

Dumb thought but swap #2 plug with #1 and see if #2 quits firing; could be a defective plug which has happened before. Good luck

 

[AlTn]

Re: Johnson 70 firing on 2 of 3

inductive timing light on each plug wire in turn..is #1 firing a frequently as the other 2?..at tdc does #1 piston top look cleaner than the other 2?

 

[BonairII]

Re: Johnson 70 firing on 2 of 3

Dumb thought but swap #2 plug with #1 and see if #2 quits firing; could be a defective plug which has happened before. Good luck

Swap the plug wires too....could be a bad wire.

 

[clintcela]

Re: Johnson 70 firing on 2 of 3

I swapped plugs.
Swapped wires - no change.

Next time I get to it I will swap top and bottom carbs.
But the wet plug tells me that isn't going to help. Doesn't hurt and doesn't cost anything.

While I am at it I will open up the top carb and make sure I didn't leave anything out when I rebuilt it on Saturday.

I will also check the pistons at the same time.
I do that by looking through the plug holes with a bright flashlight and spinning the flywheel slowly?

Have to look for my timing light.
I'll let you know the results.

Thanks again!

 

[clintcela]

Re: Johnson 70 firing on 2 of 3

Just wanted to say that the only evidence that there is a problem is that I do not notice a change in RPM or sound when I pull the top spark plug wire.

But pulling #2 or #3 it slows down and stalls.

It cranks right up with a flick of the starter. Idles like a champ.
When I took it to the lake 2 weeks ago to see how it would do, it would only run at high RPM. It would not idle in the water. That's why I rebuilt the carbs.

Now it starts easy. Sounds much better. But no change when I pull plug wire #1.

Am I right in assuming that #1 is not firing / combusting?

 

[AlTn]

Re: Johnson 70 firing on 2 of 3

pulling the plugwire on 1 should yield the same result as pulling it on 2 or 3

 

[clintcela]

Re: Johnson 70 firing on 2 of 3

Final result:
- Timing light shows timing ok.
- Swapped upper and lower carbs.
- Now all pistons firing.
- Pulling top plug wire only changes hum of motor (boggs down a little)
- Pulling #2 or 3 stalls engine.

Thanks for all the help guys!
Probably taker her out next weekend.

 

[BonairII]

Re: Johnson 70 firing on 2 of 3

I'm dealing with the same problem on my 1977 75hp. Pulling top cyl wire didn't make engine stumble as much as pulling #2 and #3 did. Then no fire at all on #1. I swapped coils and #1 fired. Bad coil. Waiting for new coil now.

 

[clintcela]

Re: Johnson 70 firing on 2 of 3

I swapped #1 and #2 coils.
No change.

 

[BonairII]

Re: Johnson 70 firing on 2 of 3

Do you have a service manual for your motor. It has a long section on troubleshooting the ignition system. It's way too long for me to post.

Your problem is probably going to come down to power pack or stator issue.

 

[boobie]

Re: Johnson 70 firing on 2 of 3

Don't forget the timer base.

 

[clintcela]

Re: Johnson 70 firing on 2 of 3

Finally got a chance to take her out.
Now she idles like a champ. Starts right up.

But bogs and stalls on WOT.
I can run about half speed which is 10mph but when I attempt any more, it sputters and stalls.
It sounds like it is starving for gas at higher speeds.

Is there something simple to look for?
High speed jets? Any adjustment screws?

Thanks in advance.

 

[BonairII]

Re: Johnson 70 firing on 2 of 3

Did you try to bump the key(to choke it) to see if the motor picks up at all? Next time bring a spray bottle with premix in it. Have someone drive while you spray the premix into the carb throats to see if the motor picks up.

Have you cleaned carbs lately?

Did you end up getting all cyls firing before you launched? Or are you thinking this is fuel issue now and not a spark issue?

 

[clintcela]

Re: Johnson 70 firing on 2 of 3

It ran only at WOT.
Changed squeeze bulb, cleaned & rebuilt carbs, changed plugs and some fuel lines.
Now it runs fine at lower speeds and idle but won't run at WOT.

I think it is fuel-related.
Next I will rebuild the fuel pump with the kit and replace ALL fuel lines.

Anyone have a picture of how they should be run on a J70ELCRD?
Does it matter if the gas drops down to each carb or is pushed vertically up to each carb?
Would this be why my top carb is starving? The top carb is the end of the line as the gas asends up the tube.
I was thinking to reverse it so the gas drops down to the carbs.
Or could there be an air leak somewhere in the line?

 

[Daviet]

Re: Johnson 70 firing on 2 of 3

When you cleaned the carbs did you check the high speed orifices to make sure they were clean?
Fuel coming from top or bottom should not make any difference, fuel pump should supply enough fuel to keep carbs full.
Have you checked fuel pump pressure and flow?

 

[BonairII]

Re: Johnson 70 firing on 2 of 3

Are you thinking about changing the actual carbs around? The middle carb has to to stay in the middle...the other two can be swapped though.

The design of your motor is fine. Don't change anything structurally.

If you haven't changed the 3/8ths line that connects all the carbs together...make sure to do it. No sense in changing 'some' of the fuel lines...and then find out that the line that you DIDN'T change is actually the culprit.