[HSSS427]

My understanding is that it's all about where the constraint is in the system so you want the smallest diameter line at the carb, with everything in "front" of that going up one size at each major connection back toward the tank. Seems having any -6 lines in the flow before the -10 is going to limit you to the -6 flow rate. But with 2 -6 lines feeding one -10 line, then it's hard to say - would that be the equivalent of a -12 feeding a -10 and then into a -6? Also, putting the regulator near the carb makes sense as that's where you need the pressure to be regulated - going into the float bowls. And won't do you any good for the lines to the carb to be any bigger than the inlets. As for how much difference in flow, there's too much science in that answer for me :-)