The key to preventing siphoning in some engines, as jlkonn mentioned, is make sure you can completely close the throttle from the transmitter. That means that if the carb has a throttle barrel stop screw the screw should be backed out until it does not limit the travel of the carb barrel.
Just like yours, one of my UCD's has an inverted Saito 1.00 without any pumps, valves, or regulators and is trouble free.