Why does my flurocarbon leader keep breaking when tied with a double uni-knot?

Question

I am trying to connect 12lb leadline (lead removed for knot) to a 6lb flurocarbon leader but when I tie them with a double uni knot the flurocarbon breaks when pulling it tight.

I have tried a couple of times and it breaks with very little effort, I can't break the line without it being knotted.

I'm not too sure why it's breaking but it breaks at the part of the knot that is tightly coiled. Is there a better knot I can use with line this fine? I have used the technique of threading the fluro through the middle of the braid and tying an underhand knot on larger braids but it's too hard to thread with braid this thin.

I'm using sufix 832 leadline, and Seaguar blue label leader.

Answer 1

It might be cinching so tight that it is cutting or pinching the line. Whenever I need to attach two lines I use a blood knot. Fast, simple, effective.

(Image from https://swittersb.wordpress.com/)

Here is a video of how to tie: https://www.youtube.com/watch?v=q06QKib1AEQ

Answer 2

I am not an knot expert. What I do know is floro-carbon lines does not handle excessive heat well. In that sense, if you did not wet/lube your line well during the process, your line may get overheated and damaged/warped when you tightening them fast.

In addition, fluorocarbon lines don’t dissipate heat nearly as well as monofilament, which means you’ll need to take a few extra seconds when tying by wetting/lubricating your knots and make sure to cinch them up slowly. (Source)