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Old 18 July 2009, 16:44   #1
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Yamaha 50 Questions

Looking at the engine experts for this one.

Took the SR4 out today to put her through her paces however could only manage 34 knots as per GPS. The Yamaha digital tacho was reading 2700-2800 now surely that is way down on the recommended RPM range.

I know Nos had 40 knots out of his so would you say there is a problem with the gauge or is the prop fitted incorrect 11 1/3 x 13? Would 2700 rpm give me 34 knots?

Need some help guys as had a bad day on the water....hit a rock and snapped a chunk of the skeg off.....bugger.
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Old 18 July 2009, 17:01   #2
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It should be quicker than that-but I don't think those revs are right for that speed either which suggests either a problem with the revcounter or the pulse being sent to it.
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Old 18 July 2009, 17:17   #3
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It should be quicker than that-but I don't think those revs are right for that speed either which suggests either a problem with the revcounter or the pulse being sent to it.
Thanks Nos,

I have a tiny tach which i could try but if the gauge is ok how is the pulse problem rectified?

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Old 18 July 2009, 21:51   #4
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Thanks Nos,

I have a tiny tach which i could try but if the gauge is ok how is the pulse problem rectified?

It'll just be a poor contact if the pulse isn't getting through properly.
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Old 19 July 2009, 02:15   #5
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It'll just be a poor contact if the pulse isn't getting through properly.
Thanks mate, will have a look.
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Old 19 July 2009, 05:36   #6
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It should be quicker than that-but I don't think those revs are right for that speed either which suggests either a problem with the revcounter or the pulse being sent to it.
Nos,

Just wired up the tiny tach and revs mirror gauge.

Do i need to start playing around with the prop?

Many thanks.
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Old 19 July 2009, 05:51   #7
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Are you sure you've got the prop pitch correct in your earlier post? It should reach a hell of a lot more RPM with a 13" pitch on there.


How rough was it when you tested it?
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Old 19 July 2009, 06:23   #8
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Are you sure you've got the prop pitch correct in your earlier post? It should reach a hell of a lot more RPM with a 13" pitch on there.


How rough was it when you tested it?
Just checked and it is stamped 11 1/8 x 13 -G.

It was quite calm and just me that's why i was expecting a bit more.
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Old 19 July 2009, 06:35   #9
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Most odd.

Might be worth servicing the engine if it's not been done recently. Check it's running on all 3.
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Old 19 July 2009, 06:38   #10
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Nos,

Just wired up the tiny tach and revs mirror gauge.

Do i need to start playing around with the prop?

Many thanks.
Is there any possibility that it could be the wrong Tinytach for your outboard? What revs are the Tinytach / boat rev counter showing in neutral at idle? I'm guessing the revs you are getting at WOT are about half what they should be?

My experience with two strokes ended with a Yam powervalve (bike) about 15 years ago, but I would have thought if the required idle is (say) 900rpm, your outboard will either idle like a bag of nails at 500 rpm, or will stall.

If the idle appears to be smooth (well, smooth for a 2 stroke ) and the tacho(s) do indicate 500 rpm, I would still suspect the tacho.

Cheers

Chris
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