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Old 04-04-2015, 18:07   #1
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Yamaha 9.9 chruising rpm

Hello everyone. Just bought a 2004 yamaha 9.9 four stroke, high thrust and want to ask here if it's ok to drive it WOT for long period of time?

Thank you

Victor.
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Old 04-04-2015, 18:41   #2
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Re: Yamaha 9.9 chruising rpm

Hi,
I have an 8-hp Yamaha and I have run it for 72 hours continuously at 3/4 throttle, and over 24 hrs at wide open with no apparent damage. Continues to run perfectly in spite of all the abuse it's taken.
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Old 04-04-2015, 18:49   #3
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Yamaha 9.9 chruising rpm

If it is 2004... and not rebuilt, it should be broken in already....just in case you had a typo and meant 2014 and its new or it has been rebuilt .....see below

Many Yamaha 4 stroke engines have an "over revolution" system that prevents damage to the engine by preventing it from exceeding the safe WOT speed.....you'd have to call Yamaha to verify your model has that......most 4 cycle do

1st Hour Operate the engine at varying speeds up to 2000 rpms or approximately 1/2 throttle.

2nd Hour Increase the engine speed until the boat is on plane (but avoid full throttle operaton) and then back off on the throttle while keeping the boat at a planing speed.

Next 8 HoursRun the engine at any speed however avoid operating at full throttle for more than 5 minutes at a time.

After the 1st 10 HoursOperate the engine normally.

Good luck....



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Old 04-04-2015, 19:06   #4
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Re: Yamaha 9.9 chruising rpm

Yes it's 2004 and it's broken in. Wonder what yamaha meant to say ''After the 1st 10 Hours operate the engine normally'' what's normal for this engine ? The guy who sold me this motor is a mechanic with 10 years of experience fixing/ rebuilding smal outboards told me that I can run my motor WOT for as long as I want and it wouldn't hurt it, just normal wear. Not sure if he is right.
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Old 05-04-2015, 14:22   #5
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Yamaha 9.9 chruising rpm

I think you can run WOT for as long as you'd like, assuming you have the over revolution protection system.....(which means you aren't literally running WOT despite what the throttle gauge says) theoretically, you'd be limited by your fuel supply anyway which I am guessing would run out before you could damage anything, assuming all other systems are nominal (cooling and lubrication) ....wouldn't recommend running that hard ....but it's your outboard


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Old 05-04-2015, 14:40   #6
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Re: Yamaha 9.9 chruising rpm

It's not recommended to run at WOT all the time. Doing it occasionally isn't a big issue but long term, it puts wear a lot of wear on the engine.


It's not a situation where the engine will explode after 30min at WOT but you will be shortening the life of the engine.
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Old 05-04-2015, 15:03   #7
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Re: Yamaha 9.9 chruising rpm

I'd suggest cruising RPM should be around 4000 rpm.
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Old 05-04-2015, 16:11   #8
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Re: Yamaha 9.9 chruising rpm

WOT will damage the motor if it's over propped. What is the motor on ?
44's advice is good.
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Old 05-04-2015, 16:48   #9
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Re: Yamaha 9.9 chruising rpm

Bought the motor to use as a get back home motor on 26 ft. 6500 lb power boat. I truly apretiate your support everyone !
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Old 05-04-2015, 17:50   #10
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Re: Yamaha 9.9 chruising rpm

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Originally Posted by Victor75 View Post
Bought the motor to use as a get back home motor on 26 ft. 6500 lb power boat. I truly apretiate your support everyone !
You will only be wasting fuel and making noise running WOT except if you need to get somewhere before a tide change or other reason.
I would guess 5 knots would be a reasonable speed on that boat in calm conditions , maximum speed may be 6 knots.
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Old 05-04-2015, 21:07   #11
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Re: Yamaha 9.9 chruising rpm

Quote:
Originally Posted by Victor75 View Post
Bought the motor to use as a get back home motor on 26 ft. 6500 lb power boat. I truly apretiate your support everyone !

I once had a new Mercury 9.9hp on a <2500 lb sailboat and at moderate throttle I got acceptable performance.....about 7 knots while being pretty liberal with the throttle.....6500 lbs might be a little much if you expect longevity out of the outboard......unless by "get back home motor" you mean "emergency back up" in which case it could probably get you there, just not quickly.....and it might be a good idea to avoid extended WOT operation. Good Luck.....


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Old 06-04-2015, 08:14   #12
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Re: Yamaha 9.9 chruising rpm

Quote:
Originally Posted by Victor75 View Post
Hello everyone. Just bought a 2004 yamaha 9.9 four stroke, high thrust and want to ask here if it's ok to drive it WOT for long period of time?

Thank you

Victor.
I have always believed 3/4 throttle was the way do go for economy and engine longevity. Just my take on it.
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Old 07-04-2015, 15:18   #13
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Re: Yamaha 9.9 chruising rpm

So yes I'll be using it around 4000 rpm getting back home if my main engine will quit working.


Thank You for all your good replys everyone.
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Old 07-04-2015, 15:37   #14
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Re: Yamaha 9.9 chruising rpm

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I have always believed 3/4 throttle was the way do go for economy and engine longevity. Just my take on it.
I'd agree, 75% power is usually the recommended max for piston powered aircraft too. Running at WOT will I believe considerably shorten life, the possible exception is if it's a seriously de-rated motor, then WOT may in fact be 75% power or less.
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Old 07-04-2015, 15:52   #15
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Re: Yamaha 9.9 chruising rpm

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Originally Posted by a64pilot View Post
I'd agree, 75% power is usually the recommended max for piston powered aircraft too. Running at WOT will I believe considerably shorten life, the possible exception is if it's a seriously de-rated motor, then WOT may in fact be 75% power or less.

That's a good point. The old Yam 9.9 was in effect a de-rated 15. The newer ones (since about 2009?) are much smaller displacement.
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