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Old 21 April 2014, 15:10   #11
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Originally Posted by poulner6 View Post
I must say the thought of revving my engine to the max does not give me any joy will leave that one out, thank you anyhow, 3 blade prop, need to pop into marina and confirm pitch, etc
I'd expect that combo of boat/engine would have a 19" ish prop on it. IF it is a prop issue, it sounds like you are a couple of inches over.
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Old 21 April 2014, 15:15   #12
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Thank you for all your tips and info, will check prop size and confirm
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Old 21 April 2014, 15:29   #13
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Originally Posted by Nos4r2 View Post
Don't attempt this-it's a stupid thing to do that does no good and potentially can harm your motor.
What could go wrong?! What a bullshit thing to say to be honest.. An engine which is healthy should rev up without a problem in fast idle - one with the symptoms that OP has mentioned will either rev at fast idle which indicates either an issue with pitch or gearbox, or again same issue which is likely to be a combustion issue (timing, spark, compression, etc)

Listen to a yamaha Mechanic!
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Old 21 April 2014, 16:02   #14
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If you're a Yamaha mechanic, I'm never using your services. A motor with no load will hit redline with cylinders not firing.
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Old 21 April 2014, 16:06   #15
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The only way to know max wot rpm achieved on that engine is going alone with lightly loaded rib, well trimmed boat on flat calm no wind water outing. It's just a 30-45 seconds wot test, don't worry won't blow engine out. Will know instantly if need to raise revs accordingly with a less pitch prop.

Should prop that way as to achieve near max wot numbers factory stated for that engine, bear in mind that as soon you start to add more boating mates rpm will drop accordingly. Assume rib has a tach to check, right ? Check to see if you have a healthy prop if it's an old one.

LB. if you want to blow your motor fully throttle it while being on neutral, you could have a piston going through crankcase. One issue is working at load on water, other at neutral, even on water.

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Old 21 April 2014, 17:06   #16
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Quote:
Originally Posted by Nos4r2 View Post
If you're a Yamaha mechanic, I'm never using your services. A motor with no load will hit redline with cylinders not firing.


A few seconds on the rev limiter wont do a fit engine any harm & will prove whether the problem is a miss reading tacho or an overpropped engine


have you never had a boat airborne? far worse for an engine to go offload onto rev limiter then back on load when the prop grips the water

I bet there isn't a member on here who hasn't had a huge grin on hearing the engine bark as it comes clear of the water!
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Old 21 April 2014, 17:40   #17
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What would it prove reving that engine to any amount of revs in neutral. It will only have sparks on 6 cylinders after you put it into gear.
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Old 21 April 2014, 18:31   #18
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And newer engines have a neutral rev limiter. My 2005 suzuki will only go to 3000 or so in neutral.

Can you try a different tach?
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Old 21 April 2014, 20:17   #19
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Originally Posted by beamishken View Post
A few seconds on the rev limiter wont do a fit engine any harm & will prove whether the problem is a miss reading tacho or an overpropped engine


have you never had a boat airborne? far worse for an engine to go offload onto rev limiter then back on load when the prop grips the water

I bet there isn't a member on here who hasn't had a huge grin on hearing the engine bark as it comes clear of the water!
It proves nothing worthwhile,and the motor's oil delivery isn't built to deal with prolonged revving at high revs with no load. Problems under load are just as likely not to be replicated. You could even have a 50psi compression drop on 2 cylinders and it wouldnt show. As a diagnostic tool it's invalid.

(and if you're still under full throttle when the boat hits the water you need to learn to drive it)



Quote:
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What would it prove reving that engine to any amount of revs in neutral. It will only have sparks on 6 cylinders after you put it into gear.
As I said, As a diagnostic tool it's invalid.

Quote:
Originally Posted by Bigtalljv View Post
And newer engines have a neutral rev limiter. My 2005 suzuki will only go to 3000 or so in neutral.

Can you try a different tach?
Again,as a diagnostic tool it's invalid.

44mph at WOT actually sounds a bit slow to me-as though it's overpropped.
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Old 22 April 2014, 03:04   #20
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Regardles of the merits of a short blip of full throttle your inference was it would damage a healthy engine
It wont!!!!
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