[Guy]

This goes in the "How can I not know this by now" file. Our 12 kw Perkins has been getting a little touchy about starting up. So much so that I blew the glass 20 amp fuse in the Gen control box in the gen set while cranking it. I notice that even when warm, it take 2 or 3 tugs on the dash momentary switch to fire up the gen set. I have a "mystery" switch on the dash panel labeled "fuel pump" which I have not touched in our 3500 miles of travel. I am thinking it's for the gen set? If so, should it be on the entire time the gen set is on, or just for start up? When I turn it on it runs  and does not cycle off like an auto fuel injection pump.

[HoosierDaddy]

Guy,
My '78 had a Perkins but no fuel pump switch. Low pressure (2-5 psi) fuel pumps are quite common. They are used in applications when assistance is needed to get fuel to the main pump. There was a pusher-pump that supplied fuel to the main engine. My understanding is that it was for priming only. It is possible the pump is to prime the generator for starting. (especially necessary in the event of running out of fuel or after fuel filter replacement)
I would check/change fuel filters and check the injection pump solenoid to make sure it is opening quickly. Hopefully Gordon will chime in with a more professional answer!!

[bestgenman]

I've been following this conversation and don't have much experience with older Newell's with Perkins powered sets.  My input is to operate the switch (your helper operates the switch) and listen or feel the pump to see if it operates.

 All injection pumps need a positive pressure at the inlet provided by a mechanical or electric pump.  The most common problem with hard starting is no fuel at the injection pump likely caused by filters.  Lines on the suction side of the pump, even though they look good can leak air into the fuel system, not good!  Your lift pump, either mechanical or electric should be operating when the engine is running.  It is entirely likely the switch, as Dean states, is momentary for priming.  You'll know once you determine what the "mystery switch" does.  You state the switch is maintained rather than momentary, is that a correct assessment?  I can't imagine the running instructions require the pump switch to be turned on every time you start the engine, but I have been fooled many times before!! 

Otherwise, this engine should run if positive pressure is on the inlet of the injection pump unless there are stuck components in the injection pump.  This is highly unlikely.  

Let me know what you find.

[Guy]

Will do. I will have the wife get her old clothes on and locate the pump that is actuated by the maintained switch