I had a 90 coming off the fuel pump on my pickup and even with the bending tool it still wanted to kink on me. I ended up bending it in stages. I would move it with the tool a little and then set it on the floor and very gently tap on the side of the radius with a rubber mallet. Using the hammer kept it from flattening out and developing the dreaded kink. It took way longer than it should have, but it came out nice and round like it's supposed to.

On the larger bends I just bend the tubing over my knee.