Originally Posted by Diesel911

You know that the Fuel Injection Pump operates at 1/2 of the engine speed just as your camshaft does. As far as I know there is only one lobe operating the fuel supply/lift pump.

I don't know if the 617 and the 603 and so on pumps work the same as the physical designs are different.
ForcendInduction got booted off this forum and I got suspended for arguing with a member on how the 617 lift pump works.
617:
If nothing blocks the flow out all possible volume the pump can move passes out of it.
The Fuel Pressure Relief/Overflow Valve and the size of the hole (something between 1/8th of an inch to 1/16th of an inch) in it determines how much flow can go out if that and remember while that is going on the Elements are sending part of the fuel off to the Injectors to run the Engine.

You have to remember that the piston is pushed one direction by the camshaft by way of the roller tappet and rod and the spring retunes it.

But essentially what happens is as the engine goes faster the fuel flow cannot pass fast enough through the Fuel Pressure Relief/Overflow Valve and instead of spring returning the Piston for another full stroke the fuel pressure holds the spring in some stage of compression and the fuel volume is reduced. Hence in some situations it has a variable flow.