89 Yamaha 150 Pro V Rpm?

[livetofish28]

We currently have a 89 Yammy 150 pro v that will only turn 5200 rpm with a 23p mercury trophy which we got to replace our 25p yamaha which the motor would only turn 4700 with. It's on a 1999 Stratos 273 vindicator which is almost a 70 mph boat if set up right but we can't get ours up over 60. Could our hotfoot not be wide open when pushed to the floor? Or could it be a prop issue?

Tight lines

Andrew

[Lund Explorer]

You're missing too much information.

 

The Prop - You need to consider both the Diameter and Pitch.

Jack Plate - Has that setting changed? 

Trim Gauge - Set at the same point?  Are you sure it's working correctly?

Weight - Any extra weight thrown onboard recently or since you could get up to 70mph?

Hull Damage - Is there a problem of drag?

 

If, and only after you've setup everything exactly the way it used to be, and you've checked out all of other possible issues, then you can consider the worst case scenario.  That your power head isn't putting out the same horsepower it did when it wasn't 25+ years old. 

[Crappiebasser]

Um, not everyone in Georgia.

You need to answer the questions above to know but my guess is the motor is sitting too low. I had a 273 with a 150 Rude that would run 67 @ 5500. I ran a 24P Raker. I don't think 70 is going to happen though.

[Hi Salenity]

Do you have a jackplate?

[WIGuide]

Have you had your running in the 60+ range before? If not it's probably a setup issue. I'm guessing the motor is too low and is creating excess drag and also hindering bow lift. Find out how far the prop shaft is below the hull and get back to us. 

[livetofish28]

Have you had your running in the 60+ range before? If not it's probably a setup issue. I'm guessing the motor is too low and is creating excess drag and also hindering bow lift. Find out how far the prop shaft is below the hull and get back to us.

We have never had it above sixty before. We don't have a jsck plate on it currently becuase it will no longer fit into the garage if we put It on. The main question is what could be causing the rpms to be so low? The motor should be turning at least 5500 rpms and I wonder if that could be half the speed related problem not to mention the boat chimes really bad on glass calm water

Tight lines

Andrew

[Crappiebasser]

Too low a motor can be the cause of your low RPM and the chine walking.

[livetofish28]

So it should be worth putting the 6 inch plate on?

[Hi Salenity]

So it should be worth putting the 6 inch plate on?

Probably, if your motor is not high enough you won't have the RPMS or speed.

If you can tell us the prop height we could guess how close it is.

[Lund Explorer]

We have never had it above sixty before. We don't have a jsck plate on it currently becuase it will no longer fit into the garage if we put It on. The main question is what could be causing the rpms to be so low? The motor should be turning at least 5500 rpms and I wonder if that could be half the speed related problem not to mention the boat chimes really bad on glass calm water

Tight lines

Andrew

 

If you have never had it above 60mph, then why did you mention in your original post that this was a 70mph boat?

 

Your motor is designed to red-line between 5,700 - 6,000 rpm's and you running well below that IS your speed problem.  If you plan to get to 70mph, you have a whole lot of work ahead of you.  I would suggest paying a local marina or prop shop to help you work out all of these issues.

[WIGuide]

So it should be worth putting the 6 inch plate on?

You don't have to put on a jackplate to raise your engine. They provide the best adjustment because you can adjust them in smaller increments and overall they adjust a lot farther. However, the motor height can be adjusted on the transom based on how it's mounted. If you look on the mid section of the motor you'll notice there are different holes in it. These are there so you can adjust the height. I'm guessing that yours are in the top holes which means the motor is mounted as low on the transom as possible. This will create the most drag and if there is too much drag it won't allow for bow lift. That'd be the first thing I'd look at. It's quick and easy to adjust some may be able to do it at home.