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1984 mercury 115 hp no top end

Backlash49

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hello need help, motor running tops at 4500rpm, normally runs at 5400rpm ????, does not miss, no power, checks good on land, compression 125 all 6 cyc., firing on all 6 cyc., put in new plugs,fuel filter,put on two new switch box's., checked all fuel lines for leaks.????? Thanks :confused:
 
Re: 1984 mercury 115 no top end

Try cleaning the carbs maybe a rebuild,it sounds like a blocakge some where.Check the pump diaphragms for pinholes
 
Re: 1984 mercury 115 no top end

going to take it out and check the fire on all plugs when running it at top speed to make sure it is gas or fire acts like one plug not firing. but in driveway everything checks good. ??? thanks for your help i will let you no what happens. again thanks for your help, Have a great day.
 
Re: 1984 mercury 115 no top end

checked the stator in the driveway and it shows to be good ???? if the stator was going out wouldn't one of the cyc not be firing ????
 
Re: 1984 mercury 115 no top end

To test the stator cold you may get an OK reading.Try heating it with a hairdryer or heat gun then test again. There may be a break in the windings that on heating opens and continuity is lost
 
Re: 1984 mercury 115 no top end

Was it running fine on a cooler day and then you lost about 900 rpms on a very hot humid day - that would be normal. A 10% performance drop is to be expected on very nasty days.

I would go with fresh gas and new plugs. If those two get you back close to 5K with the current weather, I would consider that fine...
 
Re: 1984 mercury 115 no top end

no i have taking it out about 4 times and it does the same thing everytime. i have already put in new plugs ????
 
Re: 1984 mercury 115 no top end

Well, if the weather can't account for the loss then you have to start with basic troubleshooting.

You need to check your compression - one bad cylinder could account for the loss.

If ok, then check for decent spark at all cylinders. In general if they all have good fire at 4000 rpms then the ignition is ok. At that point both high/low speed stator coils will be putting out max power. That alone leads me to believe it's not an ignition problem.

So if the motor is mechanically sound and the ignition is working, then you only have the fuel system left.

Any number of things can cause a loss of max rpms, but pretty high on the list would be either an air leak in one of the hose or a restriction (anything from a partially clogged tank vent, to a restricted tank pick-up to a clogged fuel filter or clogged carb jet). Another component high on the hit list would be the fuel pump.

A slight perforation in the fuel pump diaphram would also cause a high end loss.
 
Re: 1984 mercury 115 no top end

Took the boat out for some checks here is what happened, boat run for the first five minutes perfect 5400 rpm then fell back to 4500 rpm then we squeezed the gas bulb did not change anything, but when you squeezed the bulb hard 4 or 5 times the gas would go back to the gas tank but it still run at 4500 rpm is this normal. so then we pulled off the motor cover and started to check if the motor was firing on all 6 cyc while running at 4500 rpm, all 6 cyc was firing. ??? need all the help i can get thanks, Ron
 
Re: 1984 mercury 115 no top end

i have the same motor it had a bad stator. i only found out because my tach would not work. When i repaired the wires & hooked it back up the motor ran very bad.I had to get a new one.You got a rotten wire some where.
 
Re: 1984 mercury 115 no top end

checked compression 125 lbs on all 6 cyc.

cooked tube pdq ???? what does this mean ?
 
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Re: 1984 mercury 115 no top end

Yup and it looks like you got away with it,those numbers are good.Reeds sticking closed and not creating the vacuum to pull the fuel is my next thought.
Pull top carb the reeds can can be pushed GENTLY with a pencil just enough to move the petals in case some of them are stuck
 
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Re: 1984 mercury 115 no top end

i dont think my carbs have reeds ??, all they have is a checkvalue ?? not sure what to look for 1984 115 mercury 6cyc
 
Re: 1984 mercury 115 no top end

rebuild fuel pump, i run the motor on land now have fuel to no. 2 cyc. ??? will take it out to see how it runs i will let you know how it goes ???
 
Re: 1984 mercury 115 no top end

It was mentioned that the " reeds rotate as you rotate the flywheel "-------------Is that true????
 
Re: 1984 mercury 115 no top end

The reeds are NOT bolted to the crankshaft !!------------------The reed block sits in the block with a dowel to keep the reed block from rotating.---Check it out carefully.
 
Re: 1984 mercury 115 no top end

:eek:My apologies,you are correct,what is even more embarrassing is that it's not that long since I tore my own block down
 
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