1992 120hp Johnson outboard

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Jlewisreckless

Recruit
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Jun 21, 2010
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The engine starts and idles great without a hitch. I can put it in Neutral and throttle all the way up and it will roar like a champ. However, when i put it in drive and throttle all the way up it will only go about 15-20 mph and obviously won't plane out. When it First started doin that it would eventually kick in and take off but now it won't even do that. Any ideas what it could be?
 
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ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: 1992 120hp Johnson outboard

The loopers can sound great running on half their cylinders in neutral, but put a load on and the missing cylinders will not carry it.

Run your compression check, then use an inductive timing light to watch for spark over the range of RPM.

Don't pull the sparkplug wires on a running V4 looper, you will blow your powerpack.

Keep in mind that if the reason that some cylinders are not working is because of fouled carburetors, then if they are not getting gas they are not getting any lubrication either.
 
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Jlewisreckless

Recruit
Joined
Jun 21, 2010
Messages
4
Re: 1992 120hp Johnson outboard

Thank you I appreciate the insight. I will defintely look into that. I'm completely lost though. How do i check the compression?
 
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ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: 1992 120hp Johnson outboard

Get a screw in compression gauge with a 14 mm short head.

Take all of the plugs out and test one hole at a time, cranking a few revolutions for each hole. Record the readings. The Cylinders are numbered top to bottom.

The readings should be within 10% of each other. You should pull the emergency lanyard so the plugs don't fire.

This will do: http://www.sears.com/shc/s/p_10153_12605_SPM211696530P?prdNo=2&blockNo=2&blockType=G2
 
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dehydrated

Petty Officer 1st Class
Joined
Dec 25, 2009
Messages
299
Re: 1992 120hp Johnson outboard

checking compression you buy or borrow a compression gauge any parts store take plugs out of cylinder screw in comp gauge fully charged battery throttle wide open and crank engine over 4 or 5 revolutions you stop go back and look at gauge easier if you got 2 people:D
 
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