Bulletin 9D-8 August, 1951 Model
"BC" Page 8
ROCHESTER PRODUCTS, DIVISION OF GENERAL MOTORS
ROCHESTER, NEW YORK
To prevent stalling during the
warm-up period, it is necessary to run the engine at an idle speed
slightly higher than that Tor a warm engine. This is accomplished by the
fast idle cam which is linked to the choke valve shaft and holds the
throttle valve open sufficiently during the warm-up period to give the
increased idle RPM, until such time as the choke valve moves to the full
open position.
While the automatic choke is in
operation, the driver may wish to advance the throttle to the full wide
open position. Since this would decrease vacuum pull on the choke piston,
thereby closing the choke valve, it is necessary to provide increased
carburetor air flow by opening the choke valve mechanically.
To accomplish this, a tang on the
throttle lever is made to contact the fast idle cam linkage at wide open
throttle position so as to partially open the choke valve
This will also relieve excess
choking on starting by allowing more air to enter the carburetor when the
engine is cranked with the accelerator held fully
depressed.