Wont rev over 2000 rpms when in the water?

sblades659

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Aug 18, 2013
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I have a 1987 Mercury 115. When its out of the water on the earmuffs it runs like it should but when you put it in the water and its in neutral it revs up like its supposed to. But when you put it in gear and give it the gas it will only go up to 1800 rpms. Already changed the gas got new plugs and cleaned all three carburetors. Nothing worked so I was wondering if anyone has had the same problem and knows how to fix it??
 

Texasmark

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Dec 20, 2005
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Re: Wont rev over 2000 rpms when in the water?

That's a tower of power I6. On muffs, you don't need any fuel to speak of as you are doing no work...HP is energy expended. Prop turning air, no energy expended. On the water you need BTUs to roll the prop against the water resistance. That means that you need fuel availability that you didn't get on muffs.

Two things come to mind: Timing issues, or fuel supply issues. Having had the year later model of that engine, and having run it out of gas at WOT I will be inclined to fuel, but.....

First of all what is the history of the engine, where did you get it, when, what was done to it, what did you do to it besides what you stated since you acquired it, how long ago did you acquire it, how did it perform when you bought it, what kind of rig are you running it on, what kind of fuel supply system do you have, have you checked the linkages to ensure that the spark continues to advance after the carb butterflies are fully opened, what kind of and pitch prop are you running, does the squeeze bulb collapse when trying to run above 1800, does squeezing the bulb above 1800 improve performance?

Do your homework and come back for help.

Mark
 

schematic

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Re: Wont rev over 2000 rpms when in the water?

also be sure you have good spark on ALL cylinders
 

Chris1956

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Mar 25, 2004
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Re: Wont rev over 2000 rpms when in the water?

If pumping the primer doesn't help it to achieve more RPMs, you could have a high speed stator winding issue. Ohm them out.
 

Georgesalmon

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Apr 14, 2012
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Re: Wont rev over 2000 rpms when in the water?

Since you had the carbs off and cleaned them, First thing I'd do is back out the idle screws on each carb a little. Not much maybe an 1/8 turn at a time. Start with the top carb, back it out, try it, then second, try it, then bottom, try it. If that doesn't fix it, start at the top again, only 1/8 turn at a time. Doesn't cost anything to try and you don't have to take anything apart.
 

Chris1956

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Re: Wont rev over 2000 rpms when in the water?

George, Usually the lean idle mixture doesn't allow the motor to get to 1800 RPM. It will die at 1200RPM. It is a useful pointer for him.
 

sblades659

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Re: Wont rev over 2000 rpms when in the water?

yeah pumping the primer didnt do anything and we tried all the with the carbs and nothing work. I just got the boat about a month and a half ago and the first time I took it out it ran perfect no problems at all. Then I had to go away for work and it sat for a week. I didnt touch anything on it and when I came home I took it out and thats when its started no working. It didnt want to start at all and when I finally did get it started it wouldnt go over 1800 rpm. Also I mix the the gas 50:1
 

Texasmark

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Dec 20, 2005
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Re: Wont rev over 2000 rpms when in the water?

yeah pumping the primer didnt do anything and we tried all the with the carbs and nothing work. I just got the boat about a month and a half ago and the first time I took it out it ran perfect no problems at all. Then I had to go away for work and it sat for a week. I didnt touch anything on it and when I came home I took it out and thats when its started no working. It didnt want to start at all and when I finally did get it started it wouldnt go over 1800 rpm. Also I mix the the gas 50:1

Real bummer man.

Good Luck,
Mark
 

Chris1956

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Joined
Mar 25, 2004
Messages
27,036
Re: Wont rev over 2000 rpms when in the water?

Well, Take a compression test. If that is good, run the ohm test on the stator. The test is on the CDIElectronics web site.
 

schematic

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Re: Wont rev over 2000 rpms when in the water?

Have you checked the spark quality yet?????
 
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