I recently got a 7.5KW marine diesel Onan generator for free. He said it hasn't been run in a while and the voltage regulator was bad(wired for 220 but said it puts out 300v).

Anyway brought it home, stuck the fuel lines in a gallon of diesel and it fired up fairly easy. I turned it on and off a a few times and it worked great. I then took the hoses out of the gas can and put the can away. I came back to it a few hours later and it took alot of cranking to start(figured it was because the fuel lines were empty). After it did start the governor hunts/surges. The engine will start to slow way down and the governor will slam on the throttle, then back off, then back one, instead of staying at a constant RPM.
Any idea what might have happened? Why would it work fine one minute then after sitting for a couple hours suddenly develop this problem?

Wants to be coddled. Perhaps there is air in the fuel system and the injector(s) need(s) to be bled?

It spilled it's seed upon the ground...

Why a company named Cummins would buy a company named Onan is just beyond me, unless, just perhaps, they have a sense of humor? Nah, not possible...

Onans have been the standard for marine generators for many years. I agree that it sounds as though the injectors need bleeding. With the older marine diesels, you have to be absolutely religious about not getting air into the lines. They are not self bleeding.

I would see if you can find a users manual on-line that will detail the bleeding procedure for that particular model of engine.

That's how they run (the older ones) with out a load. Run an electric tool on it and it should run normal.

I worked on those/ sold those for years. They are a bit grumpy, but they are strong...

Your Gen set looks like mine.

Do a search for 7.5 MDJE, there is tons of information out there including manuals,

Like mention above you need at least a 100 watt light bulb for it to generate a voltage.

thanks, I was thinking it had something to do w air in the fuel lines, it started right after I let the lines drain back. I will try to find the manual to figure out how to bleed them.

Have a look here for a start.

This is what you are looking for takes awhile to download.

What does your outlet box look like? The PO had it hardwired into his house. Right now when I take the cover off the box there are 4 identical wires(ignore the PO's splicing). Was there a electrical plug in stock?
Cover on:


Cover off:

Sorry Colin,but my Gen set is at the boat yard. There was no AC plug on the unit, just hard wired.

If your unit is a 3CR (like 7.5 MDJE 3CR) than here's how to hook it up.

For 1 phase, 2wire, 120 volts
T1 & T3 are tied together. (Hot)
T2 & T4 are tied together. (Ground)

For 1 phase, 3 wire, 120/240 volts
T1 (Hot)
T2 & T3 are tied together. (Ground)
T4 (Hot)

For 1 phase, 2 wire, 240 volts.
T1 & T4 are tied together.
T2 (Ground)
T3 (Hot)

Note:
T2 must be grounded. Any other ground will cause serious damage to exciter.

It's been many years since I wired mine and I don't remember if the wires where marks or not. Maybe Bob can provided some more information.