Yamaha 90 Engine Speed at Wide Open Throttle

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Author Topic:   Yamaha 90 Engine Speed at Wide Open Throttle

maineidyl posted 05-12-2008 05:39 PM ET (US)
I just bought a 1996 Whaler Standard with a 1996 Yamaha 90. What should the engine speed be at wide open throttle? I am only getting 4,200 to 4,400-RPM [from the engine when the boat is] fully loaded. The only info I can find on the [recommended maximum engine speed] for [a 1996 Yamaha] states from 4,500 to 5,500-RPM. That is not too specific. Is there a general rule of thumb for this motor that people in the real world are living with. I love my Whaler, just want to make sure it is set up correctly.
Thanks
Tom
jimh posted 05-12-2008 11:08 PM ET (US)
The specification of 4,500 to 5,500-RPM is the range of engine speed at which the engine can develop the rated horsepower. There is a general rule that you should set up the boat, motor, and propeller so that when the boat is lightly loaded you can reach the upper end of the range, or in your case, 5,500-RPM.
If your boat is currently set up so that the engine is only able to reach 4,400-RPM at wide open throttle (WOT), something is wrong. If the engine is in perfect tune and running properly, the most likely cause for low engine speed at WOT is a propeller with too much pitch. However, since you have just acquired this boat and motor, you really do not know if the engine is in good tune and is running properly. You probably should give the engine a tune-up before changing the propeller.
Also, you have to adjust the engine trim properly. In order to reach higher engine speeds the engine trim generally has to be moved out a bit as speed increases. If you are operating the engine with the trim set improperly, the engine will not reach maximum speed.
After a tune-up and some further testing with the engine trimmed out, if you still cannot reach the 5,000 to 5,500-RPM range at full throttle, you should try a propeller with less pitch.
What is the pitch of the propeller you are using now?
Tohsgib posted 05-13-2008 02:59 PM ET (US)
13x17 Yamaha SS prop will be perfect when loaded.
DaveF posted 05-15-2008 08:21 AM ET (US)
I have a 1991 Yamaha 90 with the 13 x 17 prop and was wondering what what top speeds are expected with this prop? I have clean bottom paint on my boat and only see about 27 - 28 MPH.
Casco Bay Outrage posted 05-15-2008 09:05 AM ET (US)
While not an expert, I have learned a few things.
Manufactures give a 1000 rpm's as a range since it can depend on a number of variables. (air, fuel, boat, prop, elevation etc). If the engine runs below that range, at WOT it is considered "lugging". Think going up a steep hill in 4th gear, not 2nd gear. Getting to 5000 or 5200 lightly loaded would be very good.
As for your boat performance, there are 5 significant factors to determine good performance.
Model of boat
Engine mounting position (what bolt hole and where is the anti-cavitation plate in relation to the bottom of the boat)
Propeller size (i.e 13.xx by 15.)
Gear Ratio of lower unit
Weight of gear, persons and fuel
To help you set the boat up correctly, we need to know all of these. In addition, when doing performance trials, it helps running with 1/4 tank, light gear, 1 person.
When commencing a performance run, find a 1 mile section of calm water. Trim the engine all the way in (toward the transom). Accelerate to WOT. Trim the engine out till you start to see the speed fall off. If there is wind and current, do runs in opposing directions and average the results.To get accurate speed, you need to use a GPS.
Once we know all of the above, we can help
Tohsgib posted 05-15-2008 10:53 AM ET (US)
Make sure your GPS is set to MPH. My 17 with 90 Yamaha with 13x17 SS prop at 5500rpm would hit 41.5mph.
maineidyl posted 05-16-2008 11:08 PM ET (US)
Thanks for all of the replies. I am going to test following the advice given. I had approximately 420 pounds in just passengers and two 12 gallon tanks. Mine is a 96 Standard with a poling platform and rear deck. I absolutely love the boat and motor. I will pull the prop and check(I assume the pitch is printed in the hub)
Tom
Miami, FL

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Author	Topic: Yamaha 90 Engine Speed at Wide Open Throttle
maineidyl	posted 05-12-2008 05:39 PM ET (US) I just bought a 1996 Whaler Standard with a 1996 Yamaha 90. What should the engine speed be at wide open throttle? I am only getting 4,200 to 4,400-RPM [from the engine when the boat is] fully loaded. The only info I can find on the [recommended maximum engine speed] for [a 1996 Yamaha] states from 4,500 to 5,500-RPM. That is not too specific. Is there a general rule of thumb for this motor that people in the real world are living with. I love my Whaler, just want to make sure it is set up correctly. Thanks Tom
jimh	posted 05-12-2008 11:08 PM ET (US) The specification of 4,500 to 5,500-RPM is the range of engine speed at which the engine can develop the rated horsepower. There is a general rule that you should set up the boat, motor, and propeller so that when the boat is lightly loaded you can reach the upper end of the range, or in your case, 5,500-RPM. If your boat is currently set up so that the engine is only able to reach 4,400-RPM at wide open throttle (WOT), something is wrong. If the engine is in perfect tune and running properly, the most likely cause for low engine speed at WOT is a propeller with too much pitch. However, since you have just acquired this boat and motor, you really do not know if the engine is in good tune and is running properly. You probably should give the engine a tune-up before changing the propeller. Also, you have to adjust the engine trim properly. In order to reach higher engine speeds the engine trim generally has to be moved out a bit as speed increases. If you are operating the engine with the trim set improperly, the engine will not reach maximum speed. After a tune-up and some further testing with the engine trimmed out, if you still cannot reach the 5,000 to 5,500-RPM range at full throttle, you should try a propeller with less pitch. What is the pitch of the propeller you are using now?
Tohsgib	posted 05-13-2008 02:59 PM ET (US) 13x17 Yamaha SS prop will be perfect when loaded.
DaveF	posted 05-15-2008 08:21 AM ET (US) I have a 1991 Yamaha 90 with the 13 x 17 prop and was wondering what what top speeds are expected with this prop? I have clean bottom paint on my boat and only see about 27 - 28 MPH.
Casco Bay Outrage	posted 05-15-2008 09:05 AM ET (US) While not an expert, I have learned a few things. Manufactures give a 1000 rpm's as a range since it can depend on a number of variables. (air, fuel, boat, prop, elevation etc). If the engine runs below that range, at WOT it is considered "lugging". Think going up a steep hill in 4th gear, not 2nd gear. Getting to 5000 or 5200 lightly loaded would be very good. As for your boat performance, there are 5 significant factors to determine good performance. Model of boat Engine mounting position (what bolt hole and where is the anti-cavitation plate in relation to the bottom of the boat) Propeller size (i.e 13.xx by 15.) Gear Ratio of lower unit Weight of gear, persons and fuel To help you set the boat up correctly, we need to know all of these. In addition, when doing performance trials, it helps running with 1/4 tank, light gear, 1 person. When commencing a performance run, find a 1 mile section of calm water. Trim the engine all the way in (toward the transom). Accelerate to WOT. Trim the engine out till you start to see the speed fall off. If there is wind and current, do runs in opposing directions and average the results.To get accurate speed, you need to use a GPS. Once we know all of the above, we can help
Tohsgib	posted 05-15-2008 10:53 AM ET (US) Make sure your GPS is set to MPH. My 17 with 90 Yamaha with 13x17 SS prop at 5500rpm would hit 41.5mph.
maineidyl	posted 05-16-2008 11:08 PM ET (US) Thanks for all of the replies. I am going to test following the advice given. I had approximately 420 pounds in just passengers and two 12 gallon tanks. Mine is a 96 Standard with a poling platform and rear deck. I absolutely love the boat and motor. I will pull the prop and check(I assume the pitch is printed in the hub) Tom Miami, FL