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Jim McC

Motor dying under full throttle

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I have a 1990 Johnson, 25 HP outboard that I'm having trouble with. It runs great until you use full throttle for more than about 15 seconds. Then it starts to bog down and will die out if you don't back off the throttle. It also will run fine if you squeeze the primer bulb while under full throttle. It sounds like it's not getting enough gas, correct? What do you suggest? Thanks.

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replace the lines and bulb and make sure the gas tank is vented.

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Yeah, sounds like it's not getting enough gas. Just make sure you get the primer bulb installed in the correct direction. LOL! Learned that the hard way a long time ago.

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I don't think it's my tank/hose because I borrowed my friend's tank/hose, and it did the same thing. He thought maybe the fuel pump or gas filter. I don't even know if this thing has a fuel pump.

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jim, yes your motor has a fuel pump, if you have a gas tank thats in your boat and lower then your motor then you have a pump. take the cover off the engne and follow the gas line, where it hooks up to is the fuel pump, it'll go there before it goes to the carb. there is also probably a fuel filter before the pump. i would replace the filter first and try that, if it's still cutting out then i would remove the pump and check that, if thats ok then it's something with the carb, but if you have FI then it's something with the injectors.

good luck.

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The faster an engine revs, the more fuel it uses. If your engine is dying only at WOT, then it sounds like a fuel filter problem, maybe a weak fuel pump or perhaps it's just a fuel pump diaphram.

If the fuel filter is somewhat clogged, then it won't allow the needed fuel to go thru at WOT. If it's working well at all other throttle settings, I'd check the filter first.

First and cheapest thing to do is replace the fuel filter. I'm guessing that would probably take care of the problem.

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Thanks guys. I'll change the filter. I assume I need to get the filter from a Johnson dealer? The plugs were new this season.

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My motor had similar prob, I changed the fuel pump diaphrams, and it runs great.

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If you want to know for sure instead of just guessing. If you have acces to a fuel pressure gauge hook it up and watch. But my .2 cents It is deffently sounds like it is running lean. Cheap easy to replace should be replaced often anyway go ahead and put a new filter on it.

You need to know what kind of pressure you are getting from the pump or you will eventually burn the motor up. If it keeps buring out up top what kind of temps are you seeing?

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And all I can add is something way off the wall.

Have you checked your automatic safety switch?

The one the laynard is attached and that we are supposed to hook onto our PFD or shirts?

Just trying to eliminate one more area that needs to be elimnated.  :(

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I believe the fuel pump is part of the carb you could order the carb gasket kit witch would have the fuel pump diaphragm with it.

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