115 wont go past 4800 rpms

[Merganser]

I have a new 115 that I bought from local dealer where I live. They mounted and installed it.

I followed the break in by the book. At full throttle I cannot exceed 4800 rpms.

The dealer suggested I needed a higher rpm prop.

Changing the prop did not make a difference, aside from charging me $300. for changing prop and changing oil at 10 hour break in.

I was also having cavitation and lowered out board.

1 would cavitation issue contribute to not getting full rpms at WOT, I cannot exceed 4800

Second Can I just adjust the throttle cable linkage (shorten it?) to increase to proper rpms?

Are there other solutions. The dealer here is not particularly interested in investing time to help address the issue. Bought this motor for our commercial fishing boat and cannot fish until we get motor issue dialed in, so hoping for help in getting this addressed.

Thank you.

[99yam40]

No idea what motor you have or what boat.

Having pointed that out, the dealer should have a test wheel to put on the motor to test the power output of the motor to see if there is a motor problem to start out with.
If that is OK then you look at the rigging and boat itself

[Merganser]

Okay,

I will bring up to him. Motor is a brandnew 25" shaft Yamaha 115. I have a dealer here who I am learning the hard way only wants to do as little as possible.

I will ask about doing that.

[99yam40]

complete model # gives a lot of info.
Where are you located?
running in fresh or salt?
what kind of boat?
how much does it weigh loaded when testing/running?
what condition is the hull in?
what props are you talking about

[Merganser]

Motor is a 115 F115XB
Running in Saltwater, Pacific Ocean, Sitka Sound, Boat is a 22' Tolman Widebody Cabin Skiff approx dry weight is 1100 lbs, similar boats are also outfitted with a 90 hp, up to 140. With outboard and gas and gear approx 2,000 lbs (which is probably high) it has a max beam of 7' 8" It is a plywood fiberglass hull. There are no blemishes in hull. Outboard is mounted on bracket 6" behind transom.

Hull is perfectly clean it is a new boat.

Started with a 13-1/4x 17 prop

Dealer changed to 13-1/2 x 15 prop

Tests have taken place is glassy and light conditions.

Thanks for any ideas or insights.

[robert graham]

Could be a plugged injector screen on one injector....cuts your power by 25%...
I know the motor is new but maybe some debris got in there already....

[Merganser]

Okay I will look into that too, They have 12 hours and brand new fuel tanks lines, ect....

But No reason to rule anything out,

Thanks,

Josh.

[robert graham]

When my brother-in-laws f115 was running weak like yours it was a plugged injector screen....that's what made me think about it...

[Merganser]

Hard to imagine that since it was just purchased and installed last month....That being said....It could be. how old was your brother in laws 115 when it was having issues?

[Jason2tpa]

1 would cavitation issue contribute to not getting full rpms at WOT, I cannot exceed 4800

Second Can I just adjust the throttle cable linkage (shorten it?) to increase to proper rpms?

Are there other solutions. The dealer here is not particularly interested in investing time to help address the issue. Bought this motor for our commercial fishing boat and cannot fish until we get motor issue dialed in, so hoping for help in getting this addressed.

Thank you.

There was zero change in rpms when you dropped pitch by 2"?? And how about the sound of the motor at WOT....did it change with the lower pitch prop?

When you experienced the cavitation, as you put it, were you motoring straight ahead or making a hard turn? Unlikely your prop was experiencing cavitation, it being a brand new prop. Though hull imperfections related upstream can cause cavitation. Ventilation, on the other hand, is what boaters most commonly experience of these 2 phenomena. This occurs when air is introduced to water around the prop. Possible causes of ventilation are excessively high trim angle, combined with sharp turns at high rpms, rough seas, and/or a motor mounted too high on the transom.

You made this statement, "I was also having cavitation and lowered out board." What are you saying here, the engine height was lowered a notch on the transom?

The engine height plays a crucial role with engine and boat performance. Below is a picture that guides you how to determine the correct height

[Jason2tpa]

Second Can I just adjust the throttle cable linkage (shorten it?) to increase to proper rpms?

Can you? Possibly, yes. But does the throttle cable linkage require adjustment? Nope. Because it's highly unlikely the throttle cable was improperly setup at the factory. This being a brand new engine and all. IMO, I think it's a safe assumption a brand new engine has been setup properly at the factory.

Adjusting the cable will not solve the problem, rather it will cause future problems after you've determined/fixed the primary problem of not reaching spec rpm range at WOT.

It's kinda outboard mechanics 101...don't circumvent the problem by making unnecessary adjustments in order to achieve your desired engine performance. Cause when/if you do you'll have an even bigger headache down the road.

[rodbolt17]

cause your dealership sucks.
they are supposed to perform and fill out and you,the tech and a management member all sign it, you get a copy,the dealership gets a copy and Yamaha USA gets a copy.

on the PDI sheet it lists the idle speed and the WOT speed and a key number and whether or not it is system matched and a few other things.
it is a legal document.
did you get one ???

it is also why Yamaha USA does not allow loose engine sale.

[pstephens46]

I know I have said it before. Most dealers are pitiful.

[Merganser]

Thanks All for the comments and advice.

To clarify, yes I believe what I am experiencing is ventilation, as in the prop not getting bite. I explained this to the dealer who did not think that is what it was because I was not experiencing an increase in RPMs concurrent with what I describe as ventilation to dealer. I did have outboard lowered by one setting so it is now at lowest setting and I will take out today and go through testing.

as per advice I will not worry about throttle linkage, I am settings lots of advice from different sources and one person suggested that if I am at WOT and not getting full rpm range it could be a factor of cable having to much slack in it from instillation resulting in it not opening up all of the way,

Given my issue with dealer including a steering system that leaks hydraulic fluid , even after taking back to have leak fixed twice, it would not surprise me if there was something else. I will reply with results after trials today.

[99yam40]

You said there are other boats like yours around with 90hp motors on them, have you asked the owners of those boats how much speed and RPM they get and what props they use?

boats with brackets setting motor farther back away from hull usually are able to set the motor higher than the bottom of the hull.

Going deeper means more drag on the lower unit, loading the motor even more.

I would agree with the RPM not going up higher there is no cavitation /ventilating going on.
When the prop does not bite the load on motor drops and should have RPM go up.


And you did not answer Rodbolt about getting the owners copy of paper work