Yamaha F150 RPMs Rev, No Speed Increase

[REW]

Chetec,
You don't have a simple problem of having the motor trimmed up too far, or having the motor mounted too high on your boat do you?

When ever you start out, do you trim your motor all of the way down before advancing the throttle?
If not, try it.

I am just wondering if you are getting simple prop cavitation.
Since you had the problem happen on two different props, I doubt that the problem is in the propeller or the propeller attachment. I am more suspicious that you simply either have the motor mounted too high, or the motor is trimmed too high when running the engine.



Good luck
REW

[Chetac]

REW:

Thanks.

Motor was trimmed all the way down. I made sure of that this past weekend after getting advice from the board.

I didn't have this problem the first 45 hours of use.

The new prop really seemed to perform better all around with it properly torqued.

I will call a dealer and ask if there is anything else I should look at.

It's done it all 3 weekends I have used it and will be out again this weekend, so we shall see.

[Chetac]

The saga continues.

Boat ran fine Friday evening, Saturday and Sunday AM.

Sunday afternoon part way through a long boat ride it did it again, at about 2800 RPMs the RPMs shot-up with no increase in speed.

I decide I would take the prop in to get the hub checked.

When I took the prop off I also took the thrust washer off. To my surprise it was broken into 2 pieces. I don't recall if I took it off when I put the new prop on in May. I'm wondering if something happened during the winter, as it did it the first weekend out this spring with the old prop.

I bought the new prop from the propman so I called him for advice and had great service. He was quite surpised the thrust washer was broken as it is a thick part. He made some calls for me. He is thinking if the rods are bad in the hub I should have the problem all the time. In case some of them are bad, he sent me a set of rods that arrived the next day.

Replacing the thrust washer is the first thing to do and the dealer is sending a new one.

Anyone have experience with a broken thrust washer?

Why would it cause the prop to act like it does intermittently, hit about 2800 RPMs then the RPMs shoot-up with no increase in speed?

[REW]

Chetec,
I doubt very much that the broken thrust washer had any thing at all to do with the performance of your prop.

Put on a new one to see if it makes any difference.

Out of curiosity, have you ever had a bottom strike with your lower unit, or any issue with your lower unit at all?

Also, when you slide your prop on your prop shaft, you do have a good fit of the prop splines onto the splines of the prop shaft don't you?

I just wonder if you should just try a general purpose aluminum prop on your boat - to eliminate any hub issue and any other potential prop related issue with your situation.

You really need to know for sure, if this is a propeller related issue, a motor height issue, or a motor lower unit issue.

When the rpms increased, you were not turning or had just hit a wave had you? Your description really sounds very much like your prop is venting and has simply lost its bite in the water.
You don't have any fins, tabs or other things that might be dragging in the water that could be causing turbulence for your prop do you?

REW

[Esoxchaser]

I have a sneaking suspicion I know what you are going to say, but what brand prop are you running?

[Chetac]

Thanks for the help guys. Here are asnwers to the alst two questions:

Out of curiosity, have you ever had a bottom strike with your lower unit, or any issue with your lower unit at all? NO

Also, when you slide your prop on your prop shaft, you do have a good fit of the prop splines onto the splines of the prop shaft don't you? YES

I just wonder if you should just try a general purpose aluminum prop on your boat - to eliminate any hub issue and any other potential prop related issue with your situation. IT'S HAPPENED WITH 2 PROPS, THE ORIGINAL PROP, WHICH WAS FINE THE FIRST YEAR THEN ACTED-UP THE FIRST TIME OUT THIS SPRING. PROP WASN'T TOUCHED OVER THE WINTER.


When the rpms increased, you were not turning or had just hit a wave had you? NO

You don't have any fins, tabs or other things that might be dragging in the water that could be causing turbulence for your prop do you? NO. I do have a kicker motor, but it was trimmed up and I know it won't do it if it is trimmed down.

Current prop is a Powertech, but it also did it with the original Yamaha prop. Boat and motor are 2011 models and took delivery in May 2011.

Are there problems with Powertech props? That still would not explain why it did it with the old prop.

[Esoxchaser]

No issues with Powertechs that I am aware of. I run a PT on my F150. I eally expected you to say you were running a Michigan Wheel, they are known for hub issues, right out of the box.

[jrdonicht]

As REW has asked---You really need to know for sure, if this is a propeller related issue, a motor height issue, or a motor lower unit issue.
What bolt hole is your motor mounted in? Definitively could be to high. Also when the rpms shot up did it sound like the motor shot up with it. The reason I ask I have seen tachs do this and the motor stays at the same speed.

[Chetac]

Thanks guys.

I will check what hole it is mounted in. However, if it is mounted too high I would think I would have had the problem the first year I had the boat. No problems in year one. This year it has happened at least once the four weekends I have used it, but it is an intermittent problem. Something changed over the winter. It happened the first time out this spring then went away for a few days. Something changed over the winter.

Gear case lube looked perfect when I drained it.

The first time out this year was with the orginal prop. It has done it once a weekend with the new prop and there is no rhyme or reason to it (e.g. skiing, not skiing, one person, two people, 3 people, during a long boat ride, after sitting in the lift overnight or for a few hours).

The engine does sound like the RPMs are increasing, as the tach is indicating. It acts like the prop is cavitating. The first time it happened I thought there were weeds on the prop.

I'm concerned a dealer won't be able to diagnose it since it is an intermittent problem.

Anything else I should look at it?

Could it possibly be a lower unit problem? Why would it be intermittent?

[jrdonicht]

Your lower unit is gears and splined shafts,bearings. I have seen on some rotating equipment[gear boxes] where the fit is gone or the key has sheared that hold the gears on. You could put the motor in gear and grab the prop and see if you can spin it in gear. There should be some movement back and forth but you should not be able to rotate it