When you go to synthesis a Chakra Rune, it'll ask you if you're sure you want to do that and will tell you which chakra consumes which.

I know that, I have a lvl 10 orange waiting. I wanted to use it on a purple quick chakra but for some bs reason this isn't in the game. Now I'm gonna have to save for weeks to max my quick chakra

If you lock the quick chakra and not the orange one you have, you should be able to feed the orange to the quick since the game will read it as it can't consume the quick (since you locked it) and thus the only choice it has is to consume the orange. This is what I did to level my quick chakras.

I tried that before and I tried it just now, it says I need to unlock quick or that there isn't anything to synthesize

Ehm, unless you spent very few coins in inner gates or you are a very new player then there is no way that you didn't try before to feed *eless gold rune to *eful purple rune to just get the message that you couldn't do it. Why quick runes should work differently from other ones?

lvl 83, 49k power... I just plundered a lot and upgraded gear mostly and contributed to group rather than go in for 8 gates

uhmm don't worry most of the players have been to that part of the game lol