Lister Genset hunting

[kingfisk]

Hi
Last year I bought a second hand F G Wilson 3 phase genset powered by a Lister LPW3A081.
I live in a humid area, the fuel tank is metal. When first delivered it started well and then very soon smoked out and stalled. The transport had shaken up the fuel with water (and rust) at the bottom of the tank.
I replaced fuel and oil filters, oil and flushed the fuel tank, installed a water trap...all seemed well for several months using for an average of 4hrs pw a couple of hours at a time running a 3 phase table saw.
The engine now starts straight off and runs ok till warm and then starts to hunt, up to 400 rpm around the rated 1500rpm. It will hunt for 5-10 seconds then settle down for 10-15 seconds and then start hunting again.
I have replaced all fuel lines from tank to the fuel filter inlet, replaced the lift pump fuel filter and water trap filter.
The engine continues to hunt.
Does anyone suggestions to probable and /or possible causes and their remedies?

F G Wilson 12kva 3 phase build date 1998 rated rpm 1500
Cheers Richard

[dieselgman]

There are a few possible causes... does your unit have an electronic throttle control installed? If so, then the electronic controller or the actuator could be at fault. I have seen those become erratic and go in and out of synch.

Given the history with fuel contamination, you could have a fuel injection pump becoming sticky internally. Swapping out pumps is sometimes the only way to confirm if they are erratic in operation. It only takes one of the pumps with an issue to cause the whole system to lose stability.

The stock mechanical governors are sometimes very fussy and touchy on that model... also difficult to diagnose because all parts are internal and you cannot observe them directly during actual operation. In that year, the civilian models had mostly plastic governor sleeves. Those can wear and get sticky. The rack control lever can also develop a catch, look for any rough or worn area around the shutdown slider. They also used plastic bushings at key wear points... many possible places for wear to cause a gradual decay in function.

dieselgman

[kingfisk]

Thx dieselgman
Not electronic throttle control.

I did not mention that the hunting happens even when the engine is started and run without any loads (if that may make a difference to diagnosis).
Cheers

[dieselgman]

Likely culprit would lean towards governor linkages in that case. It is sometimes a pain to figure out, but close inspection of parts and trial-and-error swaps are the usual approaches. I have done a lot of parts swapping with these models. Hunting is often caused by wear on the governor sleeve at end of camshaft, also check pivot pin alignments and proper shim placements. If all else seems OK, then also make certain that the governor rack linkage block bore at the flywheel end is clean and clear of any debris. There is an expansion plug in that position to allow for thorough cleaning.

Everything in this control system must be silky smooth or the symptoms you mention will likely crop up.

dieselgman