i was surfing ebay for OS Engines and found this ridiculously expensive OS carb.... what is that round looking disc under the needle valves

http://www.ebay.com/itm/NEW-O-S-Carb...item43aa9adf2e

Seems like a fuel delivery regulator to me.[&:]

good answer...i was kinda thinking that... but i had never seen one built in the carb....the ones ive seen in pics were in the back plate

That type of carb is for their special Helicopter engines. it is used on engines like the OS Hyper 55HZ-R DRS heli-engines.

DRS system delivers fuel to the regulator under constant pressure
for precise fuel delivery throughout the entire tank from full to
empty. Mounting position of DRS is perfectly in line with the carb for
consistent operation in all attitudes of flight.
Dual needle 40L-R carburetor allows independent adjustment of idling,
hovering and high speed with four arm throttle lever for use with
a variety of servo brands.

maybe this will help.............this carb is for 2 different engines,
91HZ-R Ringed Helicopter Engine

manual is there and will explain.

http://www3.towerhobbies.com/cgi-bin...?&I=LXZGN7&P=V