Anthony, do you leave that gauge permanently in place? This from the Demon Tweeks site:
The Sytec in line fuel pressure gauges have been developed to monitor fuel pressure when making final adjustments to the fuel system. The in line gauges are available in two pressure range types, with the 1-7bar range glycerine filled, and each including a male thread for attaching to an adaptor (available separately). The gauges are designed for setting up of the fuel system only and not recommended for permanent use. (my bold). Blanking plugs are available