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Old 14-08-2011, 05:35   #1
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RPMs Drop Off

I have a Yanmar 3GMD. It starts on the first crank and runs as smooth as any diesel I've heard. The problem: when I am underway and take the RPM's to 2000 or so it will only remain at this level for a short time before the throttle slowly vibrates back dropping the RPM's to about 1500 - 1600 where it stabilizes. Apparently the PO tried to hold the throttle physically by crushing the throttle cable with clamps to increase internal friction.

Any suggestions on making a proper repair?
Duke
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Old 14-08-2011, 06:32   #2
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Re: RPMs Drop Off

Get a throttle cable brake. That is sort of what the PO tried to jury rig. It is very low tech and it is the way the cable manufacturer intended that the cable tension be adjusted.

http://www.go2marine.com/product.do?no=81150F
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Old 14-08-2011, 07:54   #3
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Re: RPMs Drop Off

This is very common on Pedestal steering systems.

Morse Makes a cable clamp specifically for this....I have also seen SS cable clamps used.
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Old 14-08-2011, 09:43   #4
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Re: RPMs Drop Off

I had the same problem and a small hose clamp on the cable housing took care of it.
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Old 14-08-2011, 10:19   #5
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Re: RPMs Drop Off

Quote:
Originally Posted by Chief Engineer View Post
This is very common on Pedestal steering systems.

Morse Makes a cable clamp specifically for this....I have also seen SS cable clamps used.
Or a bungee cord on the throttle...

Michael
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Old 14-08-2011, 10:47   #6
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Re: RPMs Drop Off

wouldnt just replacing the cable fix this?
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Old 14-08-2011, 13:57   #7
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Re: RPMs Drop Off

May not be anything to do with cables.

I had similar problems years ago and found it was down to muck in the diesel, as you increase the rpm you increase the diesel flow and increase the build up of muck in the diesel in the pipes and starve the fuel system losing rpm.

'If' this is the problem forget diesel bug cures, you just pour $ down the tank 'hoping' it will cure the problem, sorry do it once and get the tanks cleaned and all the pipework or be happy and it's just the cable!!.
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Old 14-08-2011, 20:31   #8
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Re: RPMs Drop Off

Thanks for all the input. After replacing the cables, polishing the fuel and cleaning the fuel tank, I was thinking there may be something wrong with the engine. I didn't know this is a common problem. Looks like the throttle assemblies should have an adjustment to control the cable slippage.
Again, many thanks... Duke
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Old 14-08-2011, 21:14   #9
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Re: RPMs Drop Off

Do you have a pedestal? If you do, there usually is no way to tighten the throttle movement on the pedestal.
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Old 14-08-2011, 21:23   #10
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Re: RPMs Drop Off

Quote:
Originally Posted by Chief Engineer View Post
Do you have a pedestal? If you do, there usually is no way to tighten the throttle movement on the pedestal.
Bungee cord. Sometimes simpler IS better...

Michael
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Old 14-08-2011, 21:57   #11
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Re: RPMs Drop Off

New cables have no tension at all if properly installed. Or resistance, whatever is the correct word.

Some newer pedestals have a built in tensioning screw that works on the pivot of the lever. Some older ones use a cable brake like in the link posted.

After installing new cables I chose to use a short piece of line wrapped to the pedestal roll bar and the throttle lever with push button slider like on some eyeglass lanyards.

It's easily disengaged by pulling it down off the upturned lever. It's set for 1000 rpms when pulled up onto the lever.

And the throttle is raised to cruise RPM by sliding the end on the roll bar up.

Only when full throttle is needed is it necessary to push the button on the lanyard to shorten its length. Or work the throttle by hand as normal for short bursts or docking maneuvers.

A temporary solution that works well for me, and might be permanent.
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