Little diesel running slow.

[team karst]

My port side MD2030, an old school mechanical diesel has lost rpm, even at no load. Suddenly. Actually stb machine has similar symptom. 3000 hours on the clock, i have done valve adj recently. But this rpm thing is more recent. It seems to me that loss of rpm in neutral is much more likely related to the power cable travel and the actual governor, correct? These are 3600 rpm rated, and both sit at 3000 during the max rpm test in neutral. Under prop load, these make almost 3000 each. And smooth, no smoke.
So my question. Can the rpm issue be caused by dirty injectors? Seems to me it doesnt take much power to do the no load test.

[Lepke]

In the past did the engines make 3600?
If you suspect the throttle cable, disconnect and operate the injector pump by hand. See if you get more rpm. There are adjustments for WOT on the injector pump. If you have a workshop manual the instructions are there.

Injectors can get buildups the alter the spray pattern making bigger drops that don't fully combust. But the governor should allow more fuel to maintain rpm.
If the prop or bottom is fouled it may limit rpm at the top hp.
If the engine has an air filter make sure it's clean.


Running engines at WOT under no load can cause damage.

[skipperpete]

Check the tension on the alternator belt, the tachometer pulse comes from the alternator and if the belt slips the tach reading drops.
Maybe use a phone strobe app to verify the accuracy of the tachometer.