Looked at it a little bit, seems that the 55B, C and D are all based on a Kubota engine. I rebuilt a little Phasor/Kubota generator
at the beginning of the year and it appears to have had the same integral injection/alarm system.
The solenoid should really be called a fuel run solenoid, because the oil
pressure must be high enough and the temperature low enough for the solenoid to activate and pull the fuel rack into the run position. And it does stay energized all the time the engine is on. Low oil
pressure or high temperature deactivates the solenoid, killing the engine.
I could run the little Kubota generator
without the solenoid activated by holding the fuel lever in, but from what I could see in the Westerbeke
manual, there is no way to do that on your engine.
There may be, but if there isn't, if the solenoid goes bad the engine won't run.
manual is available here:
the pertinent pages are 35, 44 and 61.
You can often buy the same parts
at substantially reduced prices at a tractor or ag equipment
Maybe somebody with experience with your specific engine can add something.