Posted for "Jabe Luttrell" <JabeLuttrell@comcast.net>:

 Hello Pat,
 
 I've seen 3/8" supply lines give roughness to a 550 engine.  The problem
 goes away with 1/2" lines.  It is necessary to abide by the mechanical pump
 suction head requirements.  Pulling fuel through the 3/8" lines, through a
 non-operating electric fuel pump and up hill to the engine (especially in a
 climb) can result violation of the minimum suction head requirements of the
 engine pump.
 
 Jabe Luttrell