Problem getting to max rpms in neutral.

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weinie

weinie

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Sep 6, 2010
1,297
Jeanneau 349 port washington, ny
The specs for my universal m18 engine indicate the maximum rpms is 3200. While the transmission is in neutral and the throttle lever is fully pushed forward, the most I get is about 2600. Otherwise, engine seems to run fine. It idles ok at around 1300 (vibrates a bit though).
Fuel filters were also recently changed.
 
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Benny17441

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May 24, 2004
7,134
CC 30 South Florida
Engine speed is controlled by a governor to help maintain constant RPM under varying loads. The governor does it by controlling the injection pump. With no load the governor will slow the engine down thus preventing it from attaining maximum revolutions in neutral.
 
GeorgiaBII

GeorgiaBII

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Jun 14, 2011
277
Hunter 22 Fin Keel Lake Martin
how are you getting your rpm readings? a gauge or a direct shot with a hand held unit?
 
weinie

weinie

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Sep 6, 2010
1,297
Jeanneau 349 port washington, ny
Benny,
I'm no mechanic, but I'm pretty sure the job of the govenor is to maintain the RPMs as the load changes. Shouldn't I be able to hit max rpms without any load?

GeorgiaBll,
I'm using my panel's tach.
 
Tom J

Tom J

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Sep 30, 2008
2,309
Catalina 310 Quincy, MA
weinie said:
Benny,
I'm no mechanic, but I'm pretty sure the job of the govenor is to maintain the RPMs as the load changes. Shouldn't I be able to hit max rpms without any load?

GeorgiaBll,
I'm using my panel's tach.
Click to expand
You may be able to rev an engine to max rpm in neutral, but do you really want to? Revving any engine that high without a load can be very detrimental to that engine's health. Put her in the water and see what she does under full throttle.
 
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Benny17441

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May 24, 2004
7,134
CC 30 South Florida
The no-load maximum RPM is usually within 10% of the engine's rated RPM. In your case 2,900 RPM would be an adequate value to attain in neutral and accept it as an indicator the engine is running well. You report the engine seems to be running well but you are only getting a reading of 2600 RPM and in such cases the first supect is tachometer error. Before doing anything you need to verify actual engine RPM. A laser type tachometer could be used for that purpose. If it were me I would put her in the water like Tom J suggests and see what she does. If you get 2600 to 2900 RPM in the water but get 5.5 knts or better in calm water your tachometer is off. If you get 3000+RPM in the water then it would be time to start checking the engine.
 
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