injector leak-off line on 4.108

[phorvati]

I'm trying to make sense out of injector return line. On westerbeke 4.108 it comes back to the top of the secondary fuel filter, very near the output that goes to the injection pump.
At the same place is the line leading to thermostart and to the tank return.
Perkins shows simmilar.
Is this how its intended to be used?
if so what if there is a very low pressure at the output of secondary fuel filter. Mainly Injection pump starving or lift pump not supplying enough.
That air would most definitely get sucked back into Injection pump via secondary fuel filter. It seems to me its very difficult to get rid of air in this section.

Calder recommends running it directly to fuel tank and capping off the fule filter end. Or putting a anti siphon valve on the way back to the fuel filter.

i am running into issues with starting westerbeke 40. When it starts it cannot idle.
Having to prime it constantly is definitely part of the problem.