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Old 06-06-2016, 18:00   #31
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

I find it hard to believe you could get 2800 tied up to the dock. Out in the water would be totally different.
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Old 06-06-2016, 19:34   #32
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

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I find it hard to believe you could get 2800 tied up to the dock. Out in the water would be totally different.

Believe me. I would follow the warm-up procedure that has been discussed in these forums regularly. So I know exactly what I am saying. Full throttle was between 2850 to 3000 rpm with black smoke, a lot of thrust in the water. Propeller is 18 x 13. Tied to the dock. Now barely making 2500 rpm and feels sluggish.


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Old 06-06-2016, 19:42   #33
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

OK then with that much black smoke and extra power the high pressure pump has either been 'wound open' or wear has given it the same effect.
Perkins have "recommended" settings for a reason to give their engines the long life they deserve.
Any competent diesel mechanic can "open up" an engine to give you far beyond the designed HP/Kw.
Perhaps your engine will last many many hours now it has the correct settings.
Maybe one size down in prop will give you added economy as well?
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Old 06-06-2016, 20:02   #34
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PERKINS 4108 LOW RPM UNDER LOAD...help!

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OK then with that much black smoke and extra power the high pressure pump has either been 'wound open' or wear has given it the same effect.
Perkins have "recommended" settings for a reason to give their engines the long life they deserve.
Any competent diesel mechanic can "open up" an engine to give you far beyond the designed HP/Kw.
Perhaps your engine will last many many hours now it has the correct settings.
Maybe one size down in prop will give you added economy as well?

I don't want to change original pump or engine factory settings. All I am trying to find out is why the engine feels so sluggish and wont reach the rpm's it used too. There are many variables that make each propulsion assembly unique. In my case with the Perkins 4108, Hurth transmission and 18" propeller ( which by the way is 3 inches smaller than the original design for my boat) my boat would cruise at 2400 rpm with a lot of reserve power in case I needed it. After 10 years of ownership and knowing the previous owner who had it for twenty years I know something is not quite right.


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Old 06-06-2016, 21:12   #35
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

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?? You mean to open one at a time to see if its any particular injector not properly functioning?


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That and also the health of that cylinder. You should see an equal drop in rpm.
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Old 06-06-2016, 21:48   #36
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

A larger propeller may allow you to achieve hull speed at a lower RPM. It may be time for an expert.
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Old 06-06-2016, 23:29   #37
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

Anthony, look at page 107 of the shop manual I sent you... it will enplane how to adjust the hydraulic max speed screw setting
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Old 07-06-2016, 00:02   #38
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

also did you bleed governor housing see N13 page 110
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Old 08-06-2016, 06:25   #39
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

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also did you bleed governor housing see N13 page 110

I bled it on the side screw. Not the top. It started right away. Do you think it could start and run with air trapped in the governor housing?


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Old 08-06-2016, 07:58   #40
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

It will start but if air is in the governor housing it will not allow the hydraulic governor to function properly. hence the low rpm.
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Old 08-06-2016, 08:16   #41
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

any air in the pump can affect the timing advance and the governorClick image for larger version

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Old 08-06-2016, 08:28   #42
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

[ATTACH][ATTACH]Click image for larger version

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Old 08-06-2016, 08:43   #43
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

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It will start but if air is in the governor housing it will not allow the hydraulic governor to function properly. hence the low rpm.

I will open the top bleed this weekend and will post the results.


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Old 10-06-2016, 09:12   #44
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

Problem Solved. It was the stop lever. The spring pulling it to the open position was a bit loose. Causing the solenoid cable to pull the lever a bit to the close position. It caused low rpm due to lack of fuel. Thanks Everyone for the valuable input. Lesson: always go after the simple things first. I guess!


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Old 10-06-2016, 10:44   #45
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Re: PERKINS 4108 LOW RPM UNDER LOAD...help!

I called this one. (See post #14)

But I am not a mechanic so don't expect this to happen every time.
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