Yamaha 50- revs?

n428 · 18 February 2009, 14:13

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

PeterM · 18 February 2009, 15:26

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

TonyC · 18 February 2009, 15:37

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

jyasaki · 18 February 2009, 16:56

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

mdt · 18 February 2009, 18:22

standard out the box brand new yam 50's efi are pulling 5800rpm after 20 or so hours.

Blizzard · 18 February 2009, 20:13

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.

n428 · 18 February 2009, 21:16

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.

mdt · 18 February 2009, 21:32

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...

outboardtech · 19 February 2009, 18:47

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 ?