How to make a double flare fuel line that does not leak

I think aluminum line is not supposed to be double flared, I have only flared it to the AN style angle of 37*(braided line connections). I would single flare it.

I suspect Putt is correct. Given that the fuel pump pressure is much, much lower than what the brake lines see, I doubt there is any need to double flare it. The Craftsman set should be good, but it is 45 deg (normal for brake lines), not 37.

But as far as brake line double flaring is concerned, my off-center flares are usually caused by the tubing end not being square and/or the flare button not being square on the end of the tube when you do the first compression.

You could measure the length of tubing you need and the fittings and and the dia and go down to your local auto parts store and get a steel one already made up and bend the angles in the tubing to make it work, they are not that expensive. All the factory lines were steel. Good Luck.

Aluminum is comparatively soft and a double flair seal relies on the stiffness of the metal tube and compression of the nut to seal properly.

Not sure if you have some available, but SS lines will hold a double flair, look as nice, if not nicer than aluminum, but are harder to bend into intricate, tight curves.

I'm not a professional bender, but I use small pulleys to bend the tubing around. Good Luck.

Its looks terribly simple, and it is, but these spring-type tools work surprisingly well for bending tubing and aren't expensive. A neighbor gave me one (not this brand) for Christmas or I would never have considered one:

https://www.ridgid.com/us/en/spring-type-tube-benders

Down side is you need a different one for each size of tubing.

I also don't think Al was meant to be double-flared. Depending upon the alloy, it may well crack before it will bend into the double-flare shape. Carb flare fittings that I have seen (when used) are just a single, conical flare like used for plumbing.

Buy the brake line flaring tool from Eastwood, its REALLY good and you will make perfect flare henceforth. I had same problems and the tool madethe difference for me, I am however unfamiliar with your flaring tool to be fair.
It was worth the money or me and I have used it much more than I thought I ever would. It does 1/4" to 3/8" lines single, double and bubble flares. check out eastwood.com

Just to double-check, I did a search on Eastwood.com and found at least two sets. One is $200, the "pro" model, and another is $32 or so. I suspect silver69 is talking about the Pro model. I don't doubt it will produce perfect flares, but it's too expensive for the few times I would use it.

Check AutoZone, most of them 'rent' those and the total cost, provided you return the rental, is ZERO.

As usual, Ivy66GT is correct. PepBoys is another place that loans tools.

If you want to buy a set, after trying a couple, including one that looked much like the cheaper one at Eastwood, the one at the link below is the one I like best. It includes a deburring tool and tubing cutter.

http://www.amazon.com/OTC-6502-Master-Brake-Flaring/dp/B0075XHDHI/ref=sr_1_1?ie=UTF8&qid=1417624916&sr=8-1&keywords=OTC+6502+Master+Brake+Flaring+Tool+Kit