Fuel supply system for internal combustion engines

In a fuel supply system for internal combustion engines, a fuel delivery pipe to which fuel injectors are mounted through respective connectors is connected to a fuel tank through a fuel connecting pipe without return piping. At least one of the connectors of the injectors is extended upwardly to open at an upper portion in the delivery pipe and has a small diameter extension pipe for enhancing sucking in air or vapor in the fuel delivery pipe into the injectors. A fuel pipe which is branched off from the fuel connecting pipe is provided above the delivery pipe, and the fuel pipe and the delivery pipe are connected with each other by a connecting orifice. The connecting orifice also extends upwardly to open at an upper portion in the fuel pipe. In the event that air or fuel vapor is generated in the fuel supply system, it is accumulated in the fuel pipe, gradually introduced into the delivery pipe through the connecting orifice, and then rapidly purged with fuel through the extended connectors and the injectors when the injectors inject fuel into an engine.