Originally Posted by Comodave
The return fuel fittings are the ones I changed. They have a large nut on them and the fittings are sorta like a flare fitting but not quite. In the photo of the engine I attached it is the hose at the bottom left with the large nut on it going into the secondaries. It is right above the hose with the 90 degree bend in it. They didn’t have an O ring.
Thanks. I figured out that the 5/16" flare that screws into the inlet has a 1/2-20 thread pitch. From your pic it seems clear that the cast secondary housing inlet seals internally at the flare (i.e. not at the nut, which would require an o-ring, or on the threads a-la npt). The weird thing is that it sure didn't seem like the 5/16" fitting I played around with screwed in far enough to seal at the flare, as it seemed to bottom out at the nut, whereas your pic shows a gap between the housing and the nut. Hmm... I'll take it with me tomorrow and see if I can figure it out.
I may go ahead and pull the trigger at McMaster-Carr on a couple of these
and see if they work since I need to order the rest of the fittings anyway. I'll call Brian beforehand; don't want to chance it with the fuel system.