1980 johnson 100 bogging under load

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Grizzboss

Recruit
Joined
Jul 17, 2012
Messages
5
Hello all, My motor is bogging real bad under wot and under a load. i have replaced the fuel pump, plugs a coil and a power pack, and it still runs like crap. it seems to run fine on the muffs but not in the. i have also cleaned the carbs. all the butterfly valves are open when the throttle is wo. It revs up fine in neutral. i had it out a few days ago and for 3 min it ran like it should then all of the sudden it started to bog down again. Please help i am at a total loss and have no other ideas on what could be causing my issue.
 
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emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 1980 johnson 100 bogging under load

You may not be running on all 4 cyls. Weak ignition components tend to fail once the engine heats up to normal operating temps. (may run fine when cold.) Check for spark once the engine is warm and it starts to have running issues. Easy to check with an inductive timing light -it will show you the quality of spark on each plugwire. (intermittents, no spark, weak spark, etc.) Any of these engines will seem to run fine on the trailer, when it is actually only may be firing on 2 or 3 cyls. You need all 4 firing when the prop is 2 feet under water and it is in gear...
 
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Grizzboss

Recruit
Joined
Jul 17, 2012
Messages
5
Re: 1980 johnson 100 bogging under load

ok ill give that a try. i did notice that one spark plug is always black and oily while the rest of them look good. any ideas on why that one plug would not be firing? i replaced that coil with a used one and it didn't make a difference.
 
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emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 1980 johnson 100 bogging under load

Usually the coils are pretty reliable. Probably better to check the power pack, stator and timer base. Those are the other components in the ignition system. All pretty expensive, so it will be worth your while to qualify each of them first and then spend the money on the part you need.
 
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emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 1980 johnson 100 bogging under load

You will need some testing specs and some electronic equipment. The original factory service manual has all that you need. You can get one from the original publisher: outboardbooks.com May also find this website an excellent reference: cdielectronics.com To perform some of these tests, you will need a special "peak-reading" voltmeter.
 
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