John Deere stx38 - Manual (Page 53)

4/23/97
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ENGINE TESTS AND ADJUSTMENTS
SLOW IDLE SPEED ADJUSTMENT
—CARB/EPA STX38 (SN 210001— )
& STX46
Reason:
To set engine slow idle mixture and rpm.
Equipment:
• JTO5719 Photo Tachometer
Procedure:
1. Move transaxle to neutral. Engage park brake.
Late Model Carburetors—CARB/EPA
IMPORTANT: DO NOT force the SLOW idle mixture
screw tight, this will damage the needle and
seat.
2. Put reflective tape on blower housing screen.
NOTE: On CARB/EPA carburetors, no preliminary
adjustment is required for black limiter slow
idle mixture screw, this is pre-set by
manufacturer.
3. Start and run engine at MEDIUM idle for 5 minutes
to obtain operating temperature.
4. Move throttle lever to SLOW idle position.
5. Use a photo tachometer to check engine rpm at the
blower housing screen reflective timing tape.
6. Turn Black Limiter SLOW idle stop screw in either
direction until specified SLOW idle speed of 1650
± 75 rpm is reached.
NOTE: It may be necessary to adjust slow idle stop
screw again.
7. Recheck slow idle stop screw setting.
Specifications:
SLOW idle stop screw setting. . . . . . 1650 ± 75 rpm
NOTE: For high altitude operation (above 4000 feet),
use high altitude carburetor kit, service part
number AM119687 (1994 and above) to
prevent over rich fuel mixture and black
exhaust smoke.
c
ATTENTION
DO NOT attempt to adjust carburetors that meet
California Air Resource Board/Environmental
Protection Agency (CARB/EPA) restrictions
unless you are a factory trained technician with
authorization to service CARB/EPA Emissions
Carburetors. These carburetors can be identified
by the black limiter on the slow idle mixture
screw.
M58370
Black Limiter
Slow Idle Mixture Screw
Slow Idle Stop Screw