Natural Gas Stationary Engine Will Not Start and Run 1

[RIMJ]

The engine is a one year old Wisconsin V465D natural gas fuelled unit [the derated hp for natural gas at 1000 feet above sea level at 1800 rpm is about 35 hp]. The driven load, a centrifugal pump has a brake hp of about 25 hp [when we can get the engine up to speed]. This engine ran without difficulty for about a year. Recently, however it has exhibited the following problem.

The engine will not start without the shutoff valve on the gas supply line being pinched almost closed. This did not use to be the case. Once the unit is idling, it can be brought up to speed by opening the shutoff valve very slowly. A tee has been installed right at the inlet to the carburettor, and a pressure gauge read while the unit is running displays rapid pulsations.

We suspect an issue with the regulator, but can anyone be more specific in the diagnosis?

Thanks in advance for any ideas.

 

[TBP]

The pulsations make it sound like an upstream PRV is hunting, which usually means it's oversized for the load. Has any work been done on this valve? Any adjustments made to it? Has the gas supply pressure to the reg been increased?