PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 1/TASK 2
situated on the side of the piston cylinder so that it will only pull the
choke valve open the desired amount before the piston will cover the vacuum
passage. This will block the passage, keeping the piston from moving any
further.
(b) Choke Piston Integral with Choke Housing. The choke piston
system also may be integrated with the choke heating system. This is done
by putting the choke piston into the choke housing. As the manifold vacuum
pulls the piston open, controlled linkage around the piston allows the same
vacuum source to pull in heated air for the choke.
(c) Remote Choke Pulloff. The remote choke pulloff is the most
common configuration in current automotive design. It is made from either
metal or plastic and uses a rubber diaphragm that pulls the choke open
through linkage. The linkage is adjustable to obtain the proper choke valve
opening. The lever on the choke shaft is slotted so it will not interfere
with full choke valve opening.
(d) TwoStage Choke Pulloff. A variation of the choke pulloff is
the twostage choke pulloff that has a springloaded telescoping pull rod.
The choke valve, in the beginning, will be pulled open only partially. As
the thermostatic coil heats and relaxes, it will be overcome by the pressure
of the spring on the telescoping pull rod and the choke valve will open
further. This design provides more precise control and is popular with
emissioncontrolled vehicles.
(7) Fast Idle Cam (figure 28 on the following page). When the choke
system is operating during warmup, the engine must run at a faster idle
speed to improve driveability and prevent flooding. To accomplish this, the
carburetor is fitted with a fast idle can operated by linkage from the
choke. The fast idle cam operates by holding the throttle valve open. As
the choke valve gradually opens, the can rotates, gradually reducing idle
speed.
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