1996 15 HP Johnson losing power

[Todtc]

Hello and thanks for putting up with my first post.

I just purchased a boat with a 1996 15 HP pull-start Johnson outboard attached to it. It ran great the first few times I had the boat out. I just cross a river to a duck club I belong to. The entire trip is maybe 20 minutes. On the third trip, I lost power but it kept running. I'm guessing I was at about 1/2 power and at idle, the engine would quit. At one point all engine power came back quickly and then died off again. It was almost as if the power "slammed" back on for a moment before slowly dying off again. I idled into the harbor, waited about 1/2 hour and then tried the motor again. It ran great for two more trips and then the same thing happened.

I changed the plugs and the engine ran great for two more trips before dying off again today. Once more I got about 1/2 power with a couple "slams" of full power but it never fully came back.

I have tried pumping the primer bulb to no avail and took apart the tank hoses to check for blockages. None. The engine seems to rev to full power in neutral when this problem is occurring.

Any suggestions on what to look at next?

Thank you!

 

[steelespike]

Re: 1996 15 HP Johnson losing power

Your probably losing one cylinder.Disconnect and ground one plug wire at a time and try it.You might check the plug wires to see if they are rubbng anyplace.

 

[Todtc]

Re: 1996 15 HP Johnson losing power

I just put the motor on the bench and removed the spark plugs. The top plug was clean. The bottom plug looked good but I could pour fuel from it when I turned it over. Do you think I am fouling this plug and losing the cylinder? If so, what is the likely cause?! The plug wires look good. Thanks again.

 

[lyncraft_mechanic]

Re: 1996 15 HP Johnson losing power

when you say the top plug was clean, does it look abnormally clean like a new plug right out of the package? if so you might have a blown head gasket, you should check your compression and spark. you can buy the spark and compression tester at your local auto parts store or some stores give you an option to rent tools.

 

[Todtc]

Re: 1996 15 HP Johnson losing power

Thanks for responding. No, the plug does not look abnormally clean. It looks like it's been run. By clean, I meant it didn't have gas pouring from its innards like the lower plug did. Does this explanation make sense or am I making matters worse?!

 

[lyncraft_mechanic]

Re: 1996 15 HP Johnson losing power

well that is a good sign, i would still test you compression and spark though to make sure. you are probably loosing one cylinder as suggested before,meaning that one cylinder is loosing spark. you probably have a coil failing when the engine warms up.

 

[Todtc]

Re: 1996 15 HP Johnson losing power

Thank you for the the knowledge. As a follow-up question, if the coil is going bad, could that affect only one plug? In other words, does the coil go bad as an entire unit or can it simply fail one plug while the other works? What is the internal mechanism that goes bad? I'm assuming heat is the culprit since I lose power only after the engine has been running for some time. Is this correct?

The "kid" at the Marine service shop said it sounds to him as though the carb is running too rich and it would be between $300-$500 to "figure it out". Wouldn't a too rich carb setting affect both plugs instead of just one? He says the fuel could just be reaching one plug if something was amiss in the carb.

Thanks for the schooling!

 

[asdasc]

Re: 1996 15 HP Johnson losing power

That kid is a rip off artist from what you have told us already!

I would check the spark plug wire connections at both ends, it sounds like one is loose.

 

[lyncraft_mechanic]

Re: 1996 15 HP Johnson losing power

you have 2 ignition coils,one per cylinder, so yeah it is possible to have one coil go bad. what usually happens is when an ignition coils start to fail, the fiberglass like resin that insulate the coil itself develop cracks overtime, so when the engine gets up to tempature the heat expands the cracks and allows the spark that is supposed to go to your spark plug, ground out to your engine block,causing you to loose a cylinder.
As far as that kid goes i would have to agree that he is trying to rip you off!!!!!!!! check out this website to get an idea of what parts you may need and their prices http://www.shop.evinrude.com