The Bulldog fuel system includes a boost pump which provides sufficient fuel pressure to cope with aerobatics. The engine has an 'injector carburettor' rather than a simple old-fashioned float carburettor. The intake senses air pressure demands; differential air pressure then controls a fuel metering ball valve through which fuel flows to a flow divider and thence to each cylinder. A sort of poor man's fuel injection system - but which worked well except for hot restarts on the ground which were often problematic as the flow divider became heat-soaked.
The limiting factor for inverted flight was oil pressure - normally detected by the prop rpm decreasing as the CSU went to coarse pitch with reducing oil pressure. I gather that a mod. was introduced after my time which was supposed to fix this.
The Bulldog is slightly larger and heavier than the Pup and has a 200 hp Lycoming. Ser.1 Pups had a 100 hp R-R Continental, Ser.2 a 150 hp Lycoming and the rare Ser.3 Pup 160 had a 160 hp Lycoming. Nevertheless, the additional weight and drag of the Bulldog means that there is little difference in handling characteristics between the Pup and the Bulldog which have similar wing and power loading; both have light, well-harmonised control forces and fly beautifully.
Blunty, Roger tells me that the 'dog is back and looks stunning!