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Old 27-05-2010, 05:43   #1
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Loss of Speed / RPM from New Engine

I installed a new Yanmar 4JH4E last August. We set the pitch of the max prop to achieve the engines rated max rpm of 3000 at WOT. Recently the best we can achieve at WOT is 2350 rpm. We have cleaned the hull , prop and shaft in the water but no change. We can still get the engine to 3000 in neutral and reverse but not forward under load.We currently have the injectors out for checking but have not yet had a result back from the engineers. Any ideas?
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Old 27-05-2010, 05:46   #2
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when I had a similar problem last year it was the fuel filter
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Old 27-05-2010, 05:48   #3
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I would agree, no fuel or a small air leak in the fuel line.
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Old 27-05-2010, 07:01   #4
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Did you change the size of your exhaust line?
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Old 27-05-2010, 08:52   #5
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spindrift, you say recently, have you ever been able to achieve this in forward?
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Old 27-05-2010, 09:18   #6
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I have the same engine, same prop, and the same problem. The difference is that I reset my Maxprop to what the factory recommended and have not been able to bring my boat up to the correct RPM's ever since. I am going to go back to the settings I had before to see if that is the problem. There are a few things that I can think of to check 1) Is there a fuel restriction. Check all fuel line connections and filters. and 2) Exhaust blockage. Is there any restriction on your exhaust?

As a seperate question but relevant to the thread does anyone know if the settings on a Max Prop can change once the prop has been installed?
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Old 27-05-2010, 12:30   #7
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Thanks, but the engine/prop performed perfectly for the first 250 approx hours around the South Pacific. At 2400 we cruise at 7.2 knots. We can still get the same speed at same rpm except the engine is now at WOT not as previously 3/4 throttle.I wondered if the pitch had changed, it is a max prop VP but I do not see how that is posssible. Based on threads above I will check the fuesl pressure.
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Old 27-05-2010, 14:37   #8
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As a seperate question but relevant to the thread does anyone know if the settings on a Max Prop can change once the prop has been installed?

I have a max prop on my boat(a Tayana 37) for over 25 years and have never experienced a change in pitch once set. I have experimented with the pitch when hauled out of the water in a desire to achieve a higher rpm on WOT. As to the original poster's question, it sounds like the prop or bottom is fouled even though it was cleaned in the water. If the prop and bottom is indeed clean then something must be up with the engine/tranny or maybe the tach?? I found recently that my tach was in error by using a photo tach to calibrate so maybe I need to reduce the pitch to achieve the rated rpm. Not really sure of this even though most think that being overproped is bad on the engine.
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Old 27-05-2010, 15:30   #9
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Maybe something to do with the throttle linkage?
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Old 27-05-2010, 19:01   #10
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So you are saying that the throttle is full forward......with the same RPM you had before? and your cruising speed is unchanged?

I would look at the cable/limkage before I start tearing things off the engine
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Old 27-05-2010, 20:14   #11
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A little late here but ditto Chief Engineer and Deepfrz.

Though I am not exactly sure about your rpm, speed and throttle setting at a particular point in time.
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Old 27-05-2010, 21:16   #12
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I would say it was the prop pitch. Internal parts do wear and in turn may cause a greater pitch.

First, I think I would decrease the pitch one notch before getting too involved with the motor.

PYI Inc. Max-Prop PSS Shaft Seal Seaview Radar Mounts R&D
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Old 27-05-2010, 21:31   #13
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I would say it was the prop pitch. Internal parts do wear and in turn may cause a greater pitch.

First, I think I would decrease the pitch one notch before getting too involved with the motor.

PYI Inc. Max-Prop PSS Shaft Seal Seaview Radar Mounts R&D
Hmmm,
Seems to me that if the pitch had changed, then he wouldn't get the same boat speed at his 2400 rpm engine speed as he reports.

This is an interesting one!

Cheers,

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Old 27-05-2010, 22:32   #14
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Hmmm,
Seems to me that if the pitch had changed, then he wouldn't get the same boat speed at his 2400 rpm engine speed as he reports.
This is an interesting one!
Cheers,
Jim
Mathematics say more pitch more speed. One just needs the HP to push it over hull speed. A 4JH4E only has about 55 HP, which is not a lot for a Warwick 46 displacing 14 tons.
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Old 28-05-2010, 00:13   #15
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Have you tried the "governor" setting?
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