I have a 1977 mecury 70 hp outboard that keeps leaking gas from the bottom carb. i rebuilt it and it runs fine

Question

and then all the sudden it will leaks. does anyone know why.

Answer 1

Either it has a hairline crack, that doesn't leak until it warms up and expands, or the bowl gasket is leaking.

Answer 2

there's one other possibility ,the float maybe sticking on it,and causing that too happen,it may not stick all the time,but they will occasionally stick and cause it to come out the over Flo on it,its worth checking out,make sure its not coming from the gasket also,good luck.