Sourcing new return fuel line?

JNewm

JNewm

True Classic
Hi all--

Quick question: does anyone know the diameter/size of the (bigger) return/low-pressure hard fuel line for FI X1/9s? And/or do you have a preferred source for hard fuel lines? MWB sells used ones, but I'd like to make a new one if possible. Thank you!
 
When I was making new lines for my turbo application I measured the fittings on the fuel rail as M12 (1.25) inlet and M14 (1.5) outlet. Like so many parts on these cars they are a little unusual size fittings. I converted them to connect flex hoses in place of hardlines, which came to 3/8" inlet hose and 5/16" return hose. But unfortunately I don't have the dimension for the stock hardline, however it is close to those.
 
So the inlet hose is bigger than the return hose? Good to know! I'd been thinking it would be the other way 'round, since the return one is low(er) pressure... Interesting. Thank you!
 
No, I'm only saying that's what I used when I converted mine to hoses. I needed to maximize fuel supply. I don't recall what the stock sizes are. But there will be more fuel volume going into the fuel rail than coming out of it, so the return line could be smaller. However I think they are the same size?

Also the fitting sizes are relative to the actual junction; the inlet goes directly to the rail, the outlet comes off the pressure regulator. So the fitting sizes don't necessarily relate to the line sizes. I believe some years had a different inlet connection - a barb "slip-on" fitting for the hose vs a threaded fitting? Again, not sure.

However all of this isn't too relevant if you want to make new lines. So long as you find a way to match the fittings on the ends, any size tube (within reason) will be fine for a stock setup. That's why I listed the fitting sizes.

Sorry if I confused things more than helped.
 
The interface from the fuel rail/pressure regulator to the return line uses 7.5mm fuel line like the inlet. Same at the end of the hard return line to the tank is also 7.5mm ID. Again low pressure so it doesn’t need to be injection fuel line.
 
Just to confirm what Karl said. 7.5 mm for both supply and return lines. I have two extras if you decide you want a used one.
 
Rodger said:
Should work just fine.
Click to expand...
Hm, the plot thickens. Here's the line I got from MWB (on the left) vs. an OEM return line (on the right). The MWB line is clearly quite a bit smaller in OD.

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And it's also substantially smaller in ID.

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Maybe just buy some 5/16" line at a parts store and use that?
 
On the fuel injection tank I got from Chris Obert (don't recall the year it came out of), the supply line outlet is 7/16" OD and the return inlet is 5/16" OD. In both cases I am converting to 3/8" hard line tube with AN fittings. Finding 7/16" hose barb/AN6 male adapters was difficult, but I did find them.
 
Mark Olson said:
On the fuel injection tank I got from Chris Obert (don't recall the year it came out of), the supply line outlet is 7/16" OD and the return inlet is 5/16" OD. In both cases I am converting to 3/8" hard line tube with AN fittings. Finding 7/16" hose barb/AN6 male adapters was difficult, but I did find them.
Click to expand...
That's exactly what I was referring to in my first post about the line and fitting sizes. I did the same, converted the fittings to a different type to allow the use of standard size lines and connections. But the rest of my fuel supply system is non-stock, so it also made things easier all around.
 
Sorry @JNewm , I don't think we've offered you a good answer. I'm wondering if some FI X's came with a different size return line than others? No idea. If you still have your old lines then the safest thing is to match them exactly. That way it will fit the fittings you have. As far as the fittings go the outside diameter of the pipe is want matters, not the inside diameter. So to use the existing fittings you will need to find a pipe (hardline) that is the same OD as the old one. Otherwise I'd consider not using hardlines and convert the fittings to use fuel hoses instead.
 
I'd say you don't want line smaller than 6mm ID for fuel delivery. Shouldn't really be an issue for the volume requirements of the small displacement/ low HP setups like the X1/9, however safer not to use smaller than that, so I wouldn't use 5/16" line....
 
Thanks for all the advice, all. Much appreciated! @lookforjoe, wouldn't 5/16" OD line meet that standard though? I found some at JEG's (e.g.) that has an ID of 0.257 in (6.528 mm).
 
You could use flexible line the entire distance from the tank to the fuel pressure regulator.

In any case the hard line is as I stated 7.5mm hardline as yours shows from your measurement.

Did your old one rust through?
 
kmead said:
Did your old one rust through?
Click to expand...

It hasn't rusted through yet, but when I was replacing a brake line I noticed it's horrifically rusty down toward the "bottom", where it's getting close to the tank. I used to live on gravel roads in the Midwest. I also need to replace the hard line going *to* the fuel rail, as that one's rusty as well. Less clear how/why that one rusted, though it is up against a rusted shock tower--I guess it could have "caught" the rust from there? At any rate, they're making me increasingly nervous with each passing day. Thanks for the tip re: flex line! I may go that route, as I happened to order a bunch of it from a Porsche supplier. MWB's website notes quality issues with some 7.5mm braided hose, but I figured those Porsche guys would scream bloody murder if they weren't getting super high quality stuff.
 
Well, I'm a bit stuck, but on the inlet side of things. I (incorrectly) figured the stock flare nut would work with 5/16" tube, so I could just bend up a whole new inlet line and flare it, using the stock nut. But the stock nut (presumably with an ID of 7.5 mm) is just a bit too small to fit onto 5/16" line. Of course, like an idiot, in order to remove the nut I cut the flared end of the old inlet hard line off too short for it to be reusable. Compounding the problem, I don't have a way to flare 7.5 mm hard lines. Worse yet, I don't see that size listed for sale at local parts stores--I can't even seem to find them online at vendors like McMaster-Carr. So, basically, right now I have the flexible line that's attached to the fuel rail with a female fitting, but no way to attach an inlet line to it.

So it looks like I'm on to either Plan B or Plan C, or _______(?).

Plan B: (Is this a dumb plan?) Could I buy something like this, which is described as an "M12 x 1.5 to 5/16 hose barb fitting"? And then just screw it into the stock flex-hose-to-fuel-rail female fitting? And then just run a rubber hose from the fuel filter to the barbed end of this fitting?

1615067310982.png


Plan C: @Rodger, you mentioned above that you have a used return line... Is there any chance you have a non-rusted supply hard line you'd be willing to sell + ship my way?

Plan D: ________? Is there some other way I might proceed?
 
"Plan B" is what I did. However the fittings needed are a little bit special for the Fiat (go figure). They look exactly like the one you pictured, but they have a slightly different taper inside the threaded end to fit the other half on the fuel rail. Also a different thread pitch than you listed. I found the correct ones. If we can confirm that yours are the same as mine then I can send you a link where to get the needed fittings. I'll need some good pictures of all of your fittings to start with, then maybe some measurements. I sent you a PM.
 
By way of update, I hit upon a maybe smart/maybe dumb solution. The stock fitting was *so close* to being able to fit onto the 5/16" line that I figured I might as well try drilling it out just a bit, The goal was to see whether I could get it to fit without eliminating so much material as to make it dangerous. I definitely got it to fit, and I think(?) it's not dangerous. Obviously not an ideal solution, and I'll plan to replace it at some point down the road, but I think this works for a medium-run fix.

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