The nipple that is by the carb adjustment screws (opposite side of the cylinder - I would call it the bottom) is for the primer hookup. If you decide not to use the primer (I didn't - works great!) - simply plug it off. The fuel inlet is the other nipple (on the top - by the cylinder) - that's the one you want. I used 1/8" I.D. fuel line for mine - just make sure that the tubing is for gasoline!!! You probably should also use some sort of a retainer on the fuel line - (like zipties, or maybe even safety wire) - to keep them from inadvertantly coming off at the wrong time