John-deere stx38 User Manual download pdf (Page 62)

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4/23/97

FUEL AND AIR SYSTEM REPAIR

ENGINE

INSPECT CARBURETOR

1. Disassemble bowl, float, inlet needle, low idle

mixture screw and spring.

IMPORTANT: Further disassembly of carburetor is

not required for general cleaning. Further

disassembly will require replacing parts with

new parts. DO NOT soak carburetor in

carburetor cleaner when fiber, rubber or foam

gaskets are still installed. Cleaner may damage

these components.

2. Clean carburetor using pressurized carburetor

cleaner and compressed air. Clean out all

passages.

3. DO NOT remove idle port welch plug unless

absolutely necessary. To remove, pierce with

sharp tool. Clean chamber. Install new plug using

a flat tool about the same size as plug. Flatten plug

but do not force below the surface of the cavity.

4. If inlet seat was leaking or damaged it can be

replaced by pulling it out with a drill bit or screw.

Always replace with new parts. Press in new seat

until it bottoms in bore.

5. If throttle and choke plates were removed, use a

high strength thread lock and sealer on the small

retaining screws. Install screws slightly loose.

Apply pressure on shafts to center plates in bore,

then tighten screws.

IMPORTANT: STX38 Serial Numbers

(STXH271285—272591 Gear)

(STXJ270811—272392 Hydro)—Float may stick

in carburetor bowl due to main jet not being

flush with carburetor body, this can cause fuel

in crankcase and exhaust. Inspect and repair

carburetor main jet as required. Removal of

carburetor is not necessary. You will be able to

feel the jet with your finger, or visibly see it, if it

is not completely pressed in. If main jet is not

completely flush, press jet flush to carburetor

body using a flat blade screwdriver and pliers.

6. Main jet can be pressed out. Replace with new jet

(high altitude jet is available). Press new jet in until

flush with surface.

7. Low idle mixture screw has a precision taper. If

screw is grooved, bent or broken this may indicate

seat damage and carburetor may need to be

replaced.

8. On standard carburetors, to set preliminary

adjustment for idle mixture screw—

turn

clockwise until LIGHTLY seated and back

out

(counterclockwise) one full turn

CARB/EPA Carburetor

9. On CARB/EPA carburetors, no preliminary

adjustment is required for idle mixture screw (A),

this is pre-set by manufacturer—

only turn screw

(limited to maximum 1/4 turn in either

direction) until specified slow idle speed is

obtained (see Slow Idle Speed Adjustment,

earlier in Tests and Adjustments group of this

section)

Specifications:

Carburetor Float Bowl Cap Screw . 6 N•m (55 lb-in.)

CAUTION

Gasoline is explosive. Do not expose to flame or

spark. Serious injury can result. DO NOT expose

them to flame or spark. Follow the cleaner

manufacture’s warnings and instructions on its

proper and safe use. Never use gasoline as a

cleaning agent.

Choke Shaft

Throttle Shaft

Seal

Choke Spring

Body

Choke Plate

Throttle Plate

Idle Screw

Fuel Screw

Main Jet

Inlet Seal

Needle

Float

Float Bowl

Solenoid

M52127

Optional

Fuel Shut-Off

M58370

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John-deere stx38 User Manual Page 62

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