[QUOTE]"When its warm and I shut off the WUR using the tap on the pressure gauge, the engine runs better."

By closing off the control pressure from the WUR, you are reducing the control pressure at the metering piston in the FD. Reduced control pressure results in a richer mixture.

[QUOTE]"If I remove the airpipe from the manifold to the WUR, the engine speed increases."

When you remove the airpipe (vacuum line?) you signal the WUR that the manifold pressure has increased to atmospheric pressure, which is a full load condition, and the response of the WUR is to reduce control pressure to provide a richer mixture.

Please note that in both of these scenarios, improved running of the engine is the result of providing a richer mixture.