ENGINE DIVISION SERVICE MANUAL
observe the following additional precaution:
Idle mixture adjustments must be made as soon as
possible after engine wi1ll run without choke (choke plate
fully open) before sufficiently high to cause evaporation of
winter grade gasolines. Enrichment of the idle mixture by
fuel evaporation can be detected by observing test meter
readings. Readings should remain stable. A gradual
increase in engine idle speed (RPM) or a tendency for the
CO meter to climb toward the rich side without any
adjustments being made indicates a richening of the
mixture due to fuel evaporation. When this condition
occurs, engine should be allowed to cool before making
final mixture adjustments.
Connect tachometer to engine. (Tachometer should
have an expanded scale of 400 to 800 or 0 to 1000
RPM and 1 to 2% accuracy).
Fig. 59 Exhaust Analyzer - SE-2507
Disconnect air injection hose(s) at air manifold check
valve(s) and plug air manifold check valve(s).
Operate engine until it reaches normal operating
temperature (unless winter grade gasoline is used).
Adjust curb idle speed to specifications (see
Emission Control System Tune-Up Specifications).
Prepare Exhaust Analyzer SE-2507 or equivalent,
and insert exhaust sample probe into vehicle's tail
instructions for preparation and hook-up procedures.
indicated on analyzer dial and adjust idle mixture
screw(s) to obtain specified CO setting (see
Emission Control System Tune-Up Specifications), if
Readjust idle speed, if necessary, and readjust
mixture screw(s) to provide the specified CO setting
at the specified speed.
If specified CO setting cannot be obtained, establish
proper mixture screw(s) setting as follows:
(1) Remove limiter cap(s). To prevent damage to screw
threads or seat, file or grind away the side of the cap.
Do not pry cap off.
(2) Gently seat idle mixture screws.
(3) Adjust idle speed and mixture screw(s) (equal
number of turns) to provide the specified CO setting
at the specified speed.
(4) Install new plastic (service limiter cap(s) with tab in
reconnect air injection hose(s) to air manifold check
Adjustment Procedure without Exhaust Analyzer.
For U.S.A. (except California) and Canada engines.
Idle speed and fuel mixture adjustments must be made
with parking brake applied, air cleaner in place, transmission
in neutral and air conditioning "OFF".
CGES-215 Page 33
PRINTED IN UNITED STATES OF AMERICA