“So how do you know how much fuel is enough?”

My plastic bottles have permanent marker lines showing 1 fl. oz. steps. I usually pour that much per meal (2+ cups). I use the open-jet stove the most.

“a few of the stoves I have made don't stay lit or need alot of preheat fuel, I'm not sure what I'm doing wrong,…”

A few things can cause this:
1. Stove is made too tall. If using a pepsi stove, 1” high works well.
2. using steel or TI instead of aluminum.
3. Or anything else that makes your stove end up being a big heatsink.

-Barry