Fuel system diagnosis and solution-Air was the problem

 In the end I found it was air and not dirty fuel that was causing my occasional problems. How do I know? I temporarily installed a clear hose from the first valve to the primary filter and I was getting bubbles. Who knows how many other places I was getting air, but that was all I needed to know. For this reason, I went in and simplified my fuel filtration and upgraded some things. I had previously tore out the prior three way valves that I now know are not great. I removed the new three way valve shown before that was relatively cheap from Amazon and used one I got from McMaster Carr that is much better with flouroelastic seats and high resistance to vacuum and pressure. I replaced my old Racor 500 with a new model that uses ORB hose barbs instead of tapered hose barbs. ORB uses Orings and I upgraded the orings that came with the parts I ordered to Viton. Viton is even more resistant to fuels and solvents of various types. 

The final set up

The orings were hard to specify and here is the information for anyone else interested: 

A 3/4-16 (-08) male ORB (O-Ring Boss) fitting uses an AS568-908 O-ring. In the hydraulic industry, the standard for ORB O-rings follows a simple rule: the size is 900 + the dash size of the port. Since a 3/4-16 thread corresponds to a -08 dash size, the correct O-ring is a 908. 

Key Specifications for AS568-908

• Inner Diameter (I.D.): 0.644 inches (16.36 mm).
• Cross Section (Thickness): 0.087 inches (2.21 mm).
• Outer Diameter (O.D.): 0.818 inches (20.78 mm).
• Hardness: Typically 90 Durometer (Buna-N or Viton) is used to handle high-pressure hydraulic applications. 

The fiittings on the Racor are this size and type:

90-Degree Steel Adapter, 3/4-16 (-08) Male Adjustable ORB x 3/4-16 (-08) Female ORB, 5000psi × 4

This is an elbow and then you add a hose barb that is also 3/4-16 ORB of whatever size, in my case 3/8. 

I removed the second filter altogether, as it just added fittings and valves and complications. I have never seen the vacuum gauge on my primary Racor get up anywhere near a plugged filter, and so this simplification makes sense on Aeolus, given the work I've done to clean and repair my fuel tank and all I do to keep the fuel clean with BioBor and Startron. Besides using Renewable Diesel that is not hygroscopic! Love that stuff. 

All new fuel hoses. Had to change the fuel barbs on the Walbro to 3/8, which was easy. So now it is 3/8 hose everywhere except from the fuel tank to the three way valve. Why do I have a three way valve you ask? I don't need one there. But the fuel tank fitting is 1/4 and this lets me convert it to 3/8. Eventually I will remove and replace the fuel tank fittings to make them 3/8 as well. 

Here you can see the three way valve. Out of the shot is the fuel tank. 

I plan to leave the bleed valve cracked open just enough to allow a continuous flow of fuel and any air out of the secondary filter and fuel system back to the tank. That's another thing, I used to always leave that closed up tight. No need to do that. The Walbro is rated to 18,000 hours and can run continuously at full pump speed. I'll never get close to that in the lifetime of the boat, having only put 2,000 hours on the diesel in about 18 years.