ROCHESTER CARBURETORS
Bulletin 9D-7 August, 1951
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Bulletin 9D-7 August, 1951 Model
"BB" Page 8
ROCHESTER PRODUCTS, DIVISION OF GENERAL MOTORS, ROCHESTER, NEW YORK
To accomplish this, a tang on the
throttle lever is made to contact the fast idle cam linkage at wide upon
throttle position so as to sufficiently open the choke valve. This is also
called a choke unloader and serves to dechoke a flooded carburetor during
cold starting operation.
This choke unloader will also
relieve a flooded condition on starting by allowing more air to enter the
carburetor and mix with the excess gasoline in the manifold whenever the
engine is cranked with the accelerator held fully
depressed. |
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CHOKE MODIFIER |
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The choke system, as used on some
Model "BB" Carburetors, also incorporates a choke
modifier.
The purpose of the "BB" choke
modifier, as required by certain
engines, is to prevent "loading up" or excessively rich
mixtures during the warm-up period.
Under normal operating
conditions, the automatic choke assumes a position where the torque
of the thermostatic coil is balanced against the vacuum pull on the
choke piston plus the air velocity against |
CHOKE
MODIFIER |
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the offset choke valve. As
the |
Figure 8 |
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heat from the exhaust
manifold relaxes the tension on the thermostatic coil, the choke
valve gradually opens.
When the engine is started cold
and the throttle is opened considerably (such as in going up a steep
hill), vacuum drawing heat to the coil may not be sufficient to heat and
relax the coil before some "loading up" takes place. The choke modifier,
being linked directly to the throttle, (Figure 8) is actuated by this
throttle movement. It in turn rotates the thermostatic coil, thus relaxing
the tension on the coil and allowing the choke valve to open sufficiently
to prevent "loading up". |
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