Belive it or not, you can gain better gas mialage by not letting your tank go below 1/2 full, someone that worked at Hunter with my grandfather, we did test it on an EFI vehicle and it did improve MPG by about 5 MPG, supposivly the gas builds up preassure in the tank when there is less of it and supposivly ( just what I was told ) will force more fuel into the induction system, it almost seems like it would be even more effective on a carburation system. I'm not so shure on the reason myself ( I'm kinda doubting what the guy told me ) but, it does increse MPG.