Generator won't run full revs

[Jolly Roger]

My Kubota three cylinder 120 volt diesel genset suddenly decided to only run on tick-over, and obviously won’t spin the generator. I’ve had the injectors tested and changed the fuel filter, then bled it carefully—still it won’t accelerate to normal running. It accelerates immediately it starts up, then after about ten seconds drops down to tick-over. Any ideas please?

[The Blue Heron]

Have you checked the Gen/Shore power switch? Turn it to Off and let it run for a few minutes before switching to Gen Power on Electric power source switch..

[Jolly Roger]

Hi Blue Heron: I assume you mean to start the genny with the shore power switch in the “off” position, when the genny will run on tick-over, then switch it to “ship”. Is the idea to try to jump the genny into full power, or what?

[The Blue Heron]

Jolly,

Exactly. Invertor could be stopping a surge or stopping it from engaging motor.

Doubtful a fuel control issue because you get it to start and it stays running right? That makes me suspect an electric problem with load.

[Jolly Roger]

Well that should be easy enough to do when I get back to the boat at the end of the week. I'll let you know.

[Jolly Roger]

Since we are discussing a possible electrical reason why the damn thing won’t run properly, I have to confess I fitted a new starter/run switch a month ago. The old original had seized up with the key stuck in the switch. This was a manufacturers genuine replacement switch and I was very careful to replace the wires to exactly the same terminals. After this the genny did run properly and it has only been recently that it started to only tick-over. So I assumed it would be nothing to do with my work, but then you never know….. By the way, the terminal wires were not the same configuration as in the owners manual, but I figured if it ran properly before, I should replace them where they came from. These Nip instruction books are not the most accurate to follow.

[Sailmonkey]

When it goes to tickover (idle) is it smooth or rough?
There are two thing that can cause this, fuel starvation or governor adjustment. I'll bet fuel starvation.

Do you have an electric pump or a mechanical pump for the fuel supply?

[Jolly Roger]

Wow! maybe we are getting there. It actually struck me that it was quite a rough idle, but it's previously always gone straight to main revs and not idled. And yes, I have an electric pump which seems to be ticking at the same speed, and fuel sperts out of the bleed valves.
I've also recently changed the fuel filter, so I don't think there will be any blockage in the lines, but perhaps the pump is not giving the pressure. But then, why would it run correctly for a few seconds, then idle?
I've also has the injectors checked and whilst they were not perfect, they were within specifications, so I didn't buy new.

[Sailmonkey]

If the pump is failing, or has some sort of a screen that is plugged, the fuel flow would be insufficent to allow the engine to run at speed once the initial "charge" is depleted.

Think of it like this, you have a garden hose and just barely crack open the valve. When you plug the end of the hose the pressure in the hose builds up slowly to the same pressure as the water in the pipes, when you unplug the end of the hose you get a burst of water that quickly turns to a trickle.

Now take the fuel going to the engine. If the pump is failing or has a fuel restriction somewhere, The generator is supplied with sufficient fuel pressure for a short duration then begins to starve. I'd be willing to bet you have either a plugged screen in the pump, or a pump that is on it's last legs.

[Podjo]

Some electric fuel pumps have a replaceable fuel filter. I would removed the electric fuel pump and break it down or replace it.

[Jolly Roger]

Smokemoney’s analogy is a good one, and it sounds like a second possible scenario. It always seemed to me the pump looked like it was probably original equipment. I don’t think it has any built in filter though, but it’s possible the pipes might be blocked. I will buy another pump and see if that does the trick. If it doesn’t a spare pump is always a good thing to have.