# Outboard low RPM problem



## sureshot006 (Sep 8, 2010)

I kno this isn't necessarily the place for this question but lots of views here.... hoping for some advice.

My grandpa picked up a 2008 16' sylvan with 60hp merc 4 stroke. Problem is, it won't even get up on plane. Won't get over 3500 rpm, period. Only 8mph! Sounds smooth though...

Might get a chance to work on it tomorrow... any specific place I should start? Spark? Fuel? Throttle?

Thanks!


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## DoubleJay (Aug 9, 2009)

sureshot006 said:


> I kno this isn't necessarily the place for this question but lots of views here.... hoping for some advice.
> 
> My grandpa picked up a 2008 16' sylvan with 60hp merc 4 stroke. Problem is, it won't even get up on plane. Won't get over 3500 rpm, period. Only 8mph! Sounds smooth though...
> 
> ...


Sounds like it is starving for fuel.....check your primer bulb and fuel lines. And, of course, there is always the chance that it wasn't properly winterized and the fuel soured, damaging the seals, seats, etc., which would call for a carb rebuild.....

Jay


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## DoJigger (Dec 30, 2010)

DoubleJay said:


> Sounds like it is starving for fuel.....check your primer bulb and fuel lines. And, of course, there is always the chance that it wasn't properly winterized and the fuel soured, damaging the seals, seats, etc., which would call for a carb rebuild.....
> 
> Jay


Agree with that !! After you change the fuel line and primer bulb , fuel filter , fresh gas , add some sea foam , spark plug , you might get lucky before the carb rebuild..good luck


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## Mike Gage (Oct 3, 2008)

Carb. Or potentially Upper or lower jets. 


Posted using Outdoor Hub Campfire


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## BigWoods Bob (Mar 15, 2007)

Had a similar problem....fuel pump was bad.


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## sureshot006 (Sep 8, 2010)

Thanks guys. Will start with plugs (should be done regardless) and work the electrical/fuel from there).

Coils maybe?


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## ESOX (Nov 20, 2000)

Copious quantities of Seafoam.


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## fsamie1 (Mar 8, 2008)

That is a tough one because you are saying it runs smooth at 3500 rpm. It would not run smooth if it was coil or plugs or any ignition problem. if it is filter, bad gas, clog jets, water in gas tank, it still will not run smooth at 3500 rpm. If it is running smooth up to 3500 rpm, it is the fuel filter. good luck


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## iFishy (Mar 31, 2014)

fsamie1 said:


> That is a tough one because you are saying it runs smooth at 3500 rpm. It would not run smooth if it was coil or plugs or any ignition problem. if it is filter, bad gas, clog jets, water in gas tank, it still will not run smooth at 3500 rpm. If it is running smooth up to 3500 rpm, it is the fuel filter. good luck


+1 on the filter - fuel flow is adequate up to 3500 rpm, anything above - not enough and starved... my 2 cents


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## sureshot006 (Sep 8, 2010)

Will try some seafoam and maybe fuel filter. I know my 2 cycle merc starts more reliably with seafoam after sitting for a while. Well worth it when you're 8 miles out.


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## fsamie1 (Mar 8, 2008)

I also check the throttle cable and make sure it opens all the way and nothing blocking it.


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## Lucky Dog (Jul 4, 2004)

If you are hitting 3500 R's and only going 8 mph, I'd look for a spun prop.
3500 should be well on plane.


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## sureshot006 (Sep 8, 2010)

Throttle cable looked good.

Good point about the prop...will have to check that too. It would go over 8 if it would plane out but doesnt have the balls to plane.

The previous owner had installed a hydrofoil. With that it was able to plane, just barely, and then get up to a whopping 15 mph with one guy in the boat. Still 3500 rpm tho.


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## Lucky Dog (Jul 4, 2004)

What prop does it have on it?


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## sureshot006 (Sep 8, 2010)

12x22
1.83:1

Headed out on saginaw bay in the other boat this morning. Beautiful day.


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## Lucky Dog (Jul 4, 2004)

sureshot006 said:


> 12x22
> 1.83:1
> 
> Headed out on saginaw bay in the other boat this morning. Beautiful day.



That seem like way too much pitch to me. I would expect a 13 to 15 on a 60 HP motor.

Edit. Mercury prop selector suggests a 17 pitch prop.


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## 850XP (Sep 13, 2012)

X2! You should start looking at getting a 17 pitch prop or smaller and take into count how much weight is going to be in the boat also. Remember the more weight to get on plane requires a lower pitch prop. Also a 4-blade prop will help with getting up on plane better.


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## sureshot006 (Sep 8, 2010)

Didn't have time to go over the motor today after fishing (9 eyes, most 18-20" with one 26". I think 26" is master angler in Saginaw bay  but.... I did rev the motor in neutral up to 5500 rpm. Not sure if that tells anything.

May have to try lower pitch prop... that is a huge difference. Do you think it just doesn't have the power to get past 3500 rpm with that prop?


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## Lucky Dog (Jul 4, 2004)

sureshot006 said:


> May have to try lower pitch prop... that is a huge difference. Do you think it just doesn't have the power to get past 3500 rpm with that prop?


No you do not have enough power.
My 225 HP can't even push a 22" prop.


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## sureshot006 (Sep 8, 2010)

OK update... the sticker on the cavitation plate says 12x22. Assumed that was prop specs. Seeing as a 22 pitch prop should be fairly obvious compared to a 13 I managed to decipher the part number 816702A40p12

Looks like 10.75" 12P.

Looking for fuel/spark problems now. Prop would have been so much easier!


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