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Old 18 February 2009, 09:13   #1
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Yamaha 50- revs?

Yamaha 50hp 4 stroke. High thrust

Only reving to 4000rpm- doesnt seem that high. Cant locate engine handbook. Is this right? On a 5m (approx) RIB.

Cheers
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Old 18 February 2009, 10:26   #2
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Not 100% sure what the differance is between high thrust & std ( possible gearing differance ) - got the 'normal' 4s 50 (2006) on my Avon 4m - most I've ever seen is 5200 which seems about right to me. 4000 seems to low by far - you must only be getting some way to max HP - no where near the 'full' 50.

I think they are supposed to run to around the 5500 level. I'll look at the books tonight unless someone pops up before to answer properly
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Old 18 February 2009, 10:37   #3
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I know it sounds silly, but make sure youve got the right Tacho.

Our Honda maxes revs at 4500 or so on the tacho, but switching it out with a tacho froma sister engine showed it was actually reving 5900.

Just a thought
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Old 18 February 2009, 11:56   #4
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Appears to me that all tha Yam 4-stroke 50's have a max rpm range of 5000-6000.

You can look up your manual by year and model (or for newer than 06, year model and serial number) here:

http://www.yamaha-motor.com/outboard...d_manuals.aspx

jky
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Old 18 February 2009, 13:22   #5
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standard out the box brand new yam 50's efi are pulling 5800rpm after 20 or so hours.
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Old 18 February 2009, 15:13   #6
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Hi

I would check your propellor spec. Sounds like your pitch is too high.
You should be at 5800 - 6000 at max trim max throttle.
I would look at a 17 K prop for this size of boat.

On the high thrust, normally its the other way round, they over rev on a small boat because of wrong prop

All this is assuming its actually running on all Cylinders.
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Old 18 February 2009, 16:16   #7
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Assume tacho is correct- it ticks over at about 1000rpm.

Running well on all cylinders- sounds fine and revs hard and smoothley up to 4krpm. Engine is approx 00/01 year. Serviced last week.

Will look at prop.
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Old 18 February 2009, 16:32   #8
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you have checked that you are getting full throttle ie: at the butterfly and not just at the big lever end? best to check the simple (and cheap) bits first...
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Old 19 February 2009, 13:47   #9
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n428 firstly mate a HIGH THRUST OUTBOARD engine is used and designed to PUSH big displacement hull , example a yacht . The yami high thrust engines are nOT made to push a small 5.00 metre rib or planing hull . The difference between the high thrust and standard motor is the gearbox and the gear ratio . The high thrust engine has a bigger diameter prop and bigger gears were as the standard engine has a smaller prop and gears . What boat is this engine on ?
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