You could hire the services of a competent gasfitter to check the supply pressures and operating pressures both at the source and the burner end – sounds to me like someone has run a pipe that is way too small in capacity to supply the correct volume of gas at the correct operating pressure required of the pit ring.
To identify the problem would not be an expensive exercise so so contact a suitably qualified and experienced gasfitter to resolve your problem – DON’T try the work yourself.
Safety is paramount with gas so hire an expert.
Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians