FL120 secondary filters fuel inlet fitting?

I’m re-doing my fuel lines and removing the mechanical lift pump in favor of an electric pump. Anyone know the fitting used by the secondary on-engine filter housing? It looks like 1/4 npt but isn’t. A 5/16” flare fitting threaded into it perfectly but doesn’t seat properly. I want to get to a 3/8” barb fitting.

Currently it has some sort of copper pipe compression fitting - was hoping to get the parts together before cracking open the fuel system. I took my spare into a parts store and they were stumped.

I just redid the whole fuel return system today. Got the fittings from Brian at American Diesel. Not sure what kind of fitting they are but they are nothing I have seen before.

Comodave said:

I just redid the whole fuel return system today. Got the fittings from Brian at American Diesel. Not sure what kind of fitting they are but they are nothing I have seen before.

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That's what I was afraid of... some weird swage fitting to accept the copper pipe I suppose. I've got one other industrial supply shop I'll check on tomorrow and then I'll give Brian a call. Bad enough I figured out my new Walbro pumps are 1/4" NPS rather than NPT. Man I hate plumbing fittings. I *think* everything else is 3/8 NPT.

Too bad you didn’t ask yesterday since then I could have taken a photo of the fittings. But now they are installed.

Comodave said:

Too bad you didn’t ask yesterday since then I could have taken a photo of the fittings. But now they are installed.

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Do you remember if the fitting had an o-ring? It appears to be straight thread.

Should have posted earlier!

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.

Comodave said:

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.

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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.

Sorry I could not help more. Brian should know what you need though.

Here's what we had on our FL135. The on on the left was the one I installed and was fighting an air leak. The one on the right is from American Diesel.

I changed over to electric pumps in mine as well. Could not find the correct fittings either. I eventually just cut the tubing and double-clamped my fuel line right to it. No muss, no fuss. I did flare the end a bit though before putting the fuel line on. It is low pressure, so am not worried about it.

Larry M said:

Here's what we had on our FL135. The on on the left was the one I installed and was fighting an air leak. The one on the right is from American Diesel.

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Yes! Nailed it - thanks a ton. That's a 5/16" 45deg flare fitting to a 5/16" hose barb. I'm using 3/8" hose so I went ahead and ordered the 90deg flare to 1/4 NPT fitting from McMaster Carr & I'll go from 1/4 NPT to 3/8.

If for some reason that doesn't work I'll clamp onto the existing copper pipe while I figure it out.

This forum is amazing.

It appears the two fittings in the photo could have started out the same. The right one has a narrower hex portion which would allow the fitting to be screwed in further. A bit of lathe work could modify a standard fitting if the other was not available.

I thought I would add to this slightly older thread. Hopefully it will help someone else.
The connection at the filter housing inlet from the lift pump on my engine (FL 2714E) was a 5/16 compression fitting. I took the suggestion offered by Antares and turned down the hex portion of a 5/16 x 3/8 JIC (37deg.) adapter and it worked perfectly. I'll try to add a couple of pictures.