Carburetor loses prime after 8+ hours

fwiw my car had the same problem when I bought it. I kept a little bottle of gas with me to pour into the carb to reprime it. One day I was caught without the bottle, but I did have a little marvel mystery oil I had been using as a fuel additive. I poured a little of the oil in the carb and started it up. It smoked for a few minutes until the oil burned off, but ever since then the carb keeps its prime.