Golden

Well David, the way the metering head works is a plunger is connected to a large flap, the engine "sucks" on the flap, pulling it up. The more the flap raises the higher the plunger goes, the plunger has cutouts in it allowing fuel to move from a pump fed chamber to a chamber feeding the injectors. The ease with which the engine can suck the plate is controlled by feeding a certain amount of fuel pressure to a chamber above the plunger. This is purely used to control plate resistance, this feed of fuel pressure goes nowhere near the injectors. So by dropping the fuel pressure above the plunger the engine can more easily "suck" it up and so for a given load (suck) you get more fuel to match. This is what is actually being done with the WUR mod, people are simply reducing the resistance above the metering head plunger. It is a bastardisation of the cold running system used on K Jet. To sum up, all it does it make the engine richer throughout the rev range.

Just to be anal it doesn't increase fuel pressure at the injectors but reduces the resistance above the metering head plunger, it is this that casues the mixture to richen. to be anal the injectors open with pressure and nothing else, so to get more fuel in you need more pressure you can also do this with the system pressure but it is not as accurate. control pressure lowering allows the air flap to open further for a given throttle setting. the flap lifting lifts the plunger and so more fuel, but there is an increase of pressure at the injectors First thanks for the welcome Stuart but the above is incorect, the pressure at the injectors is the same regardless of control pressure (i.e. WUR mod) it is only the lowering of the fuel pressure resistance above the metering unit plunger that richens the mixture. Although the pressure controlled by the WUR is called the control pressure it has nothing directly to do with the injector line pressure.

Just to be anal it doesn't increase fuel pressure at the injectors but reduces the resistance above the metering head plunger, it is this that casues the mixture to richen.