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Muskie Fishing -> Muskie Boats and Motors -> 40hp Johnson- Bogging down??? How to fix/problem
 
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Message Subject: 40hp Johnson- Bogging down??? How to fix/problem
beaverbuck1986
Posted 6/7/2016 10:07 AM (#819632)
Subject: 40hp Johnson- Bogging down??? How to fix/problem




Posts: 94


I had issues starting my 86' 40hp Johnson. At first it would run for about 6 seconds then die, it did that multiple of times. Then I got it started and it sounded funny...quieter, when I throttled it all the way up it was only running at half the typical speed. Any thoughts would be great. Let me know.
Jeremy
Posted 6/7/2016 11:05 AM (#819642 - in reply to #819632)
Subject: RE: 40hp Johnson- Bogging down??? How to fix/problem




Posts: 1149


Location: Minnesota.
Fuel filter etc.?? Just guessing, I'm no mechanic.

I'd toss your spark plug too and replace it plus drain the fuel and run a fairly rich mix of Sea Foam thru her...

Good luck.
ToddM
Posted 6/7/2016 11:40 AM (#819650 - in reply to #819632)
Subject: Re: 40hp Johnson- Bogging down??? How to fix/problem





Posts: 20248


Location: oswego, il
That's a twin cylinder are both cylinders firing? That would make it hard to start and not run at full speed.
VMS
Posted 6/10/2016 9:04 AM (#820106 - in reply to #819632)
Subject: Re: 40hp Johnson- Bogging down??? How to fix/problem





Posts: 3504


Location: Elk River, Minnesota
Hiya!!

This sounds like gummed up carbs for the most part....

Here is what I would suggest trying before going through and having carbs rebuilt.

First.... Replace the spark plugs (preventative maintenance anyway and the plugs are cheap for that motor) Check the spark on each... if one is not sparking the way it should, change the plugs to opposite boots and try again. If the same boot shows weak or no spark, you've narrowed it down to either the plug wire or the coil pack.

Second, replace the fuel filter as suggested in a previous post (again...preventative maintenance).

Third... Get two cans of pressurized sea foam. Get the motor started and warm. Remove the baffle from the front of the motor so you have access to the butterflies on the carbs. Start the motor and set the idle to about 1500 RPMs or so (high idle).
1) Take the cans of sea foam and spray into the carbs stopping here and there so the engine does not die....the engine will bog down a bit, as you do this, though. Repeat this process for a couple of minutes. After a couple of minutes have passed, then spray heavily into the carbs, killing the engine, then continue spraying for another 10 seconds into each carb.
2) Let the motor sit for a couple of hours or if you want...overnight.
3) Put everyhing back together and take the motor out and run it open. If we are lucky, the problem will be solved...if not, you will definitely have a clean top end of the engine.

If the problem persists, then it is time for a carb rebuild... Being only two of them, the rebuild is something you could take on if you are handy with a wrench...the only issue being is getting the carbs synced when you are done..

This really sounds like a carb issue more than anything...but the first steps are good steps to start with. And...being a 1986 motor, and if the carbs have not been rebuilt ever, this is a good thing to do as well... Another piece that gives you peace of mind...

Steve
apeoples
Posted 6/10/2016 5:14 PM (#820188 - in reply to #819632)
Subject: Re: 40hp Johnson- Bogging down??? How to fix/problem




Posts: 36


Location: Stone Lk Wi
I had the same motor, check the linkage between the carbs and the peice that advances the timing it's a small linkage under the fly wheel. The carbs come off real easy pull them apart clean them B-12 carb cleaner. Check compression in each cylinder you may have a stuck ring.
rich
Posted 6/14/2016 9:25 AM (#820555 - in reply to #819632)
Subject: RE: 40hp Johnson- Bogging down??? How to fix/problem




Posts: 133


I had the same issue except my motor was a '94. Put a new carb kit in and it runs great.
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