Advance arrangements

An advance arrangement for controlling timing of fuel delivery by a fuel pump for use in an engine, the advance arrangement comprising;

• an advance piston which is movable in either an advance or a retard direction to advance or retard, respectively, the timing of fuel pump delivery, the advance piston being exposed, at one end, to fuel pressure within a main advance control chamber,
• the advance piston having a supply port to allow fuel to flow into the main advance control chamber and a drain port to allow fuel to flow out of the main advance control chamber,
• a servo piston which is movable relative to the advance piston in response to speed-dependent fuel pressure variations within a servo control chamber to control opening and closing of the supply port and the drain port, thereby to permit adjustment of the timing in response to engine speed,
• a light load arrangement which is movable in response to load-dependent fuel pressure variations within a light load control chamber, thereby to permit adjustment of the timing in response to engine load, and
• a restricted flow path for restricting the flow of fuel out of the main advance control chamber through the drain port when the drain port is opened by the servo piston and the advance piston moves in the retard direction beyond a threshold amount.