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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Old 08-02-2010
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Low RPM's

I have an Universal M3 20B with about 450hrs. She runs like a top but, after being put in service this spring she will only run up to 2100 rpms. This is under load or in neutral...doesn't make a difference. There is no lag or stutter, runs fine and pushes along at hull speed
What could be the causitive factors of such an issue and is it possible that the tach is not reading correctly (although it does register the proper idle speed) thanks!
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Stupid question I guess but did the throttle cable slip or perhaps the control arm is hitting something preventing it from opening all the way.

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Never a stupid question...usually its the simple things. I wondered about that and check the cable at the engine and it is up against the stops, when running at full throtle, which still have the factory settings in place.
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Does it reach max RPM before it gets to the stop or is it linear? Might indicate a governor problem. If it is linear then a load, exhaust, timing or fuel issue.

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Forget load as I reread your first post. What is normal WOT for your engine?

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The WOT for the M3-20 is 3,500 to 3,600 RPMS according to Universals specs.....

I would look for a problem with the throttle cable, maybe slipped or a problem with the engine shut down not returning to the run posistion. After this there is a problem with the governor of the fuel injection system.

Last edited by r.furborough; 08-02-2010 at 06:42 PM. Reason: Correction
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Old 08-03-2010
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hmmm. I"ll be able to check on friday. The stop cable has been a bit buggered up...could be. Are there any in situ tests to find out if it"s the governor?
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Old 08-06-2010
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I have a universal 5424 and have the same issue. After much angst, I ordered a laser tach off ebay for about $10. Using the laser tach I determined that my boat tach was way off and I feel much better. I also believe that the prop is over pitched and will be having that adjusted this winter gaining an extra 400 rpms. One of the ways to tell if it is your prop is to see how fast you move while idling.

If you are moving at hull speed at 2100 and the engine feels normal then it is probably your tach. Does the engine sound the same? You should notice a big difference in sound if she used to run at 3600 and now only runs at 2100. Your ears will tell you if you are that far off. Vibration will too.
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