I have been mixing my own soda (Coke) for a while now. What I was told is to use a 5 to 1 ratio of water to syrup. I use a masson jar (24oz) as my measuring cup and i use four in a 5 gallon batch. i don't even know if the math works, but thats what I do.
As for carbing it. I let it sit on 25...
