When something lingers in your mind, it’s probably doing so for a reason. In this scenario, there are 2 choices: ignore it and move on or take care of it. I yielded and opted for the latter.

All the new fuel lines I’m running are -6AN, which means they have an inner diameter of 3/8″. Attaching these lines to the smaller 5/16″ factory hardlines led to a predicament. The solutions appeared to be limited. One way was to cut off the barbs on the hardlines and install a compression fitting, but I was skeptical on how much pressure such an adapter could hold. Another method was to flare the hardlines further with a special tool. I wasn’t very enticed by either of these and they were both relatively invasive.

Finally, after seeking insight from 3 separate individuals, they all reported having simply double clamped the -6AN line over the hardlines. So said why not, and joined in.

At first, I double clamped my lines on and then decided to triple clamp them to help assuage my neuroticism. Fast forward to more recently, I was doing more research on other viable options out of curiosity (going back to the whole stuck on my mind thing), and ended up calling Flyin’ Miata. They offer a big fuel kit for Miatas and had everything figured out. Apparently, there’s ONE company (Aeromotive) that makes a special 5/16″ barb to -6AN male adapter. Finally, this was something that made a lot of sense.

I decided to buy 2 of these adapters from Flyin’ Miata and had them Express mail them to me. It was hard to suck it up and redo the lines at the last minute, but I knew it would be better to take care of everything sooner rather than later. I’m sure my triple clamping would have worked fine, but it bugged me because it seemed fundamentally wrong.

I undid all my hard triple clamping work, removed the Feed line, and bought the appropriate push lock fittings. I took the opportunity to redo the Feed line entirely because it was originally mounted to the secondary rail with a straight fitting, but I switched it to a 45* fitting instead to lessen the bend in the line.

On the other end of the Feed and Return lines, I pushed on straight fittings. I purposely chose Blue for these to add contrast down by the firewall where they will be attaching to the adapter and hardlines. I think I’ve gotten quite good at installing push lock fittings now. For the Feed line, I was able to do everything off the car on my workbench, but I left the Return line attached. This meant I had to push on the straight fitting without a surface to press against, and had to do it all against my palm.


Here is everything connected back up with the new adapters in place.


Now, instead of force clamping a 3/8″ line over a 5/16″ barb… I’m using a short section of 5/16″ fuel injection hose from the hardlines to the 5/16″ barb end of the adapters, which then converts and connects normally to the -6AN straight fittings. I also Express mailed new spring clamps from Mazda to help with the process. On the hardlines, I’m using both a worm gear clamp (with a smooth underside so it doesn’t cut into the hoses too much) and a spring clamp.

Talk about one aspect of the build being drawn out… but I knew I couldn’t shortcut anything, especially when it comes to fuel.

2 thoughts on “Fuel Lines Re-Revisited

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