4 38 FlIEL lll Bl Il ETl0l fl ggE l During cranking manifold vacuum is applied to the m gz RN primary openings below the choke valve and causes METERING fuel to flow through the idle and primary main meter RODS ACDELERATING ing circuits to start the engine In addition to the fuel wmv noo flow from the main metering circuit a cranking jet i QQV g located in the air horn assembly between the primary I venturi provides additional fuel for cold engine starts il fig 4 68 Fuel flows from the secondary feed pas y sage through the cranking jet and into the primary Q I W throttle bores when the choke valve is closed We V I Q 1 ll if QM A WJ i V caauxiuc migraine E g f gh 9 Ts Ammo 1 I Q Flu 4 66 P w rEnrlchm m Circuit v re 1 ia y cnn carnn y A cold engine requires a richer fuel a1r mixture for gi CHDKE Q Ama i quick starting and satisfactory performance during PLATE the warmup period The choke circuit automatically regulates the position of the choke valve in the air Flg 4 68 Erlnlilng JII horn to provide the proper mixture throughout the en tire cold engine operation When the engine is cold the thermostatic coil in the choke cover exerts force against its lever and rotates When the engine tnl i mnnlfuld Vacuum is Chun the thermostatic choke shaft This action causes the n l d to the choke Vacuum diaphragm which is chokgvaivemc10s 4 ig 4 57 attached to the throttle body As the diaphragm is pulled in linkage opens the choke plane a specified dis tance The action of the diaphragm combined with at msnmosunc COVER mospheric pressure against the offset choke valve op poses the tension of the thermostatic coil and causes II 1 the choke valve to open slightly to prevent flooding of ii the engine This opening of the choke valve is referred lf g to as the initial choke valve clearance cursor Ill A s the engine warms up a chamber in the exhaust manifold crossover passage heats filtered air being mf I 4 drawn through the choke heat tube to the choke hous ing by manifold vacuum A thermostatic bypass valve g si which is integral with the choke heat tube helps pre g MANIFOLD vent premature choke valve opening during the early vacuum part of the warmup period The valve regulates the g passaos temperature of the hot airflow to the choke housing s Mn by allowing outside unheated air to enter the heat VA uUM S tube A thermostatic disc is incorporated in the valve which is calibrated to close the valve at 75 F and open Flu I 67 lilmlin Glrcull it at 55 F