Relevant description is in
-R44 POH Section 7, SYSTEMS DESCRIPTION, page 7-26 dated 21 FEB 2014, specifically ENGINE PRIMER SYSTEM (OPTIONAL)
-R44 IPC Ch 28 FUEL SYSTEM, Figure 28-33 on page 28.32 dated JAN 2014.
-R44 IPC Ch 28 FUEL SYSTEM, Figure 28-37 on page 28.36 dated JAN 2014 (early type, rarely seen due most having been upgraded to preceding).
There are two check valves within the primer pump itself: inlet & outlet. If, contrary to instructions, the primer pump handle is not locked after priming then a small amount of fuel can flow thru both check valves and cause rough idling; the engine with run smoother as MAP is increased (due to less fuel flow thru check valves).
Referenced documents freely available at
https://robinsonheli.com under the Publications tab.