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Old 28 July 2017, 18:45   #1
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14 ' RIB and 50HP

Hi, I tested my boat today, it is a novurania 14' with a 1991 50hp yamaha 2 stroke. Going with around 550 pounds of human and stock, the boat was going at full throttle 36km/h (22mph). I really tought the boat would have been going much faster (atleast 25-30mph).
Also, the motor is at maximum at around 2800rpm, wich seems slow for a 2 stroke at wot?

Thanks you!
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Old 28 July 2017, 20:27   #2
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Originally Posted by Snakymen13 View Post
Hi, I tested my boat today, it is a novurania 14' with a 1991 50hp yamaha 2 stroke. Going with around 550 pounds of human and stock, the boat was going at full throttle 36km/h (22mph). I really tought the boat would have been going much faster (atleast 25-30mph).
Also, the motor is at maximum at around 2800rpm, wich seems slow for a 2 stroke at wot?

Thanks you!
Sounds like you've got fuel/air problems. Ultrasonically clean your carbs, and replace all fuel lines and clamps if they're more than 5 years old.

But just to be sure, what prop size are you running?
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Old 28 July 2017, 20:36   #3
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I don't think I have fuel/ air problem, fuel filter are new and the motor is running very good! Maybe my rpm meter is off tough

How do I measure a propeller?
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Old 28 July 2017, 23:21   #4
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Measuring propellors

Google "how to measure a boat propellor". Definitely make sure your prop is not too high a pitch if your motor isn't developing full rpm at wot. Should be around 5200 rpm for a two stroke. Too long a pitch on your prop is like trying to tow a trailer up a hill in 5th gear.
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Old 29 July 2017, 05:35   #5
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I don't think I have fuel/ air problem, fuel filter are new and the motor is running very good! Maybe my rpm meter is off tough



How do I measure a propeller?


The diameter is easy enough, but the pitch it not trivial to measure. Almost all props have a number stamped on them to save you the trouble - but you might have to take it off to hunt for it (often on the surface against the engine).
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Old 29 July 2017, 12:28   #6
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Almost impossible to measure prop pitch accurately check for numbers at theroot of the blades or possibly on the boss sounds severely over propped if its running well
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Old 29 July 2017, 18:09   #7
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I've removed the propeller and the size is 10 3/8 by 13.
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Old 29 July 2017, 18:35   #8
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Not a particularly aggressive pitch I think I'd take it up to the rev limiter briefly offload see if it revs out then that'll tell you if the tacho is out
Should make just over max rated rpm I'd expect 5700 as I think max rated is 5500? If your anywhere near that you could be down on power or maybe try a smaller pitch
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Old 29 July 2017, 18:40   #9
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I am far from being a good mechanic and I am still learning how to service an outboard. However I can tell that without load it will rev up to 5500 perfectly!
I can't tell where is the rev limiter and what it look like lol
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