So I'm just getting my L head fired up after a partial over haul, rings and valves. I bought a WO carter carb on ebay rebuilt. Got her fired up, verified oil pressure roughly set timing, but hard to keep running. Seems the choke has to be on, even after warming to 180, also it cuts out at like half throttle like its starving for fuel. I have a fuel line dropped into a gas can as this is just a make sure all is good and rolling chassis complete. I have the single action fuel pump with glass bowl, I can see fuel in there all the time about half way up glass. I don't have a spacer plate on fuel pump as I understood that was only for dual action pumps with vacuum. Oh one other item I did check the float to make sure it is set to 3/8" as is correct. I know these problems can be hard to diagnose but any ideas are appreciated.

If you are getting the fuel to the carb that Bob has listed, then you will want to start looking at the carb.

The half throttle may be roughly where the 'high speed' curcuit is kicking in on the Carb.  The high speed jet might have some debree in it.

Does it smooth back out at full throttle? 

Was the Carter pre adjusted by the Ebay builder?  You may need to adjust the idle and the fuel air mixture.

Good starting points are 2 turns in on the idle adjustment...(back of the throttle linkage) and 1.5 turns out for the idle mixture...(front side spring loaded screw), then adjust from there.

Tim

I noticed underneath the metering jet or orifice, its the jet at very bottom of bowl, under that jet was a ball bearing just peaking out of the port or passage it rides in. It seemed to be binding in there or maybe its not supposed to go into the channel that comes back up side of carb. Is it supposed to ride in that port some kind of shut off in a roll over? Or does it just roll around under the jet and free float, or is the darn thing even supposed to be it there?