Abstract: An improved apparatus for feeding fuel to an internal combustion engine, said apparatus comprising a multiplicity of fuel sources that cooperate with a spill chamber that is surrounded by an overflow trough. Cooperation is by means of a feed line having an on-off valve along its length. The spill chamber feeds fuel to a fuel/air mixer that cooperates with the engine. The improvement comprises (i) a structural relationship between feed line, on-off valve and fuel flow in that the on-off valve is positiond in the feed line so that fuel is forced in a direction generally away from gravity immediately before and after passing through the valve and (ii) the feed line is fixedly positioned to direct fuel into the chamber when the valve is "on" and into the trough when the valve is "off". The invention also concerns an apparatus for measuring fuel octane numbers that incorporates the feeding apparatus just described.