84 Mercury not running right

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cjohnson4123

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Aug 23, 2009
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4
I have a 84 Thunderbolt 115 that I am having a issue with. When the boat is out of water the motor runs great. Takes the gas and turns good rpm's. When in the water the motor idle's good up to about 1/4 throttle. After that it boggs down and will not run (except idle speed). I thought it may be water in the tank so I drained the tank and cleaned it. I am leaning towards the carbs but would like some advice.
 
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Chris1956

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Mar 25, 2004
Messages
28,814
Re: 84 Mercury not running right

An out of water test is useless. It might be carbs, or high speed stator winding or compression.

Check compression on all cylinders. Has the motor ever run good for you? If compression checks out, test high speed of stator (go to CDI Electronics.com). Clean and rebuild carbs.
 
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cjohnson4123

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Aug 23, 2009
Messages
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Re: 84 Mercury not running right

It was running real got until I got gas at a Marina. Then it just would not run. Only at idle speed.
 
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Chris1956

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Mar 25, 2004
Messages
28,814
Re: 84 Mercury not running right

OK, You may have picked up some water or crud at the marina. Suck some fuel from the bottom of the tank and put in clear container. Is it sludge or water/alcohol suspension? If so, pour it off and clean the carbs.

If not check spark and compression.
 
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cjohnson4123

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Joined
Aug 23, 2009
Messages
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Re: 84 Mercury not running right

Ok thanks. There was some water in the mix. I pull and clean out the line going from the tank and the fuel pump. Water in the pump also. I will go to the carbs now. Thanks.
 
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