Occasional long crank problem

I know trust me. Just trying to do cheap stuff first instead of throwing 4K for injectors. Curious why the only sign is long crank no matter engine hot or cold. Even after 15 mins. And after couple day it starts right away every day for a week or so. Heard some people replaced injectors/cups but the problem was much simpler

 

I drained the separator today it had just a teaspoon of it. Filter lasts for long

It doesn’t seem to have it just a bit. I hope replacing that check valve on Davco will fix it but one guy in another thread was sure that failed check valve on water separator cannot cause fuel drain from system unless there is air getting in somewhere after it

 

Yes I do. The overflow valve on D13 is on the front side of the head. Has been replaced in first place but didn’t help

 

Sorry I may don’t get it right. I’m 100% sure I’m loosing prime in the system. The mystery is where that happens. I have primer pump on the main filter housing and when the pressure is good you can barely push it back down. What exactly can be checked with primer hand pump?