Carburetor - Aisan 2-bbl Toyota 4Runner I

DESCRIPTION

Carburetor is a 2-barrel downdraft design with primary and secondary venturi. An automatic choke containing a bi-metallic spring, controlled by a ceramic heater, provides proper air/fuel mixture control during engine warm-up.

Secondary throttle valve is actuated by a vacuum diaphragm unit with a kick-up (open) lever. Secondary valve begins to open when primary throttle valve opening exceeds 50°.

A thermostatic valve provides airflow under secondary throttle valve, when ambient air temperature is high, to maintain proper combustion. Other features include a choke opener, a main and an auxiliary accelerator pump (AAP), a secondary slow circuit fuel cut system, a fast idle cam breaker, a deceleration fuel cut system, outer vent control valve and idle-up diaphragm.

CARBURETOR IDENTIFICATION

ADJUSTMENTS

Note. For all on-vehicle adjustments not covered in this article, see TUNE-UP article in the TUNE-UP section.

Note. Manufacturer recommends using carburetor adjustment kit No. 09240-00014 for carburetor measurements and adjustments.

FLOAT LEVEL

Remove air horn gasket, invert air horn, and allow float to hang by its own weight. Measure clearance between top of float and air horn. Clearance should be.386" (9.8 mm). Adjust clearance by bending float arm at tab "A". (Scheme 85)

Float Level Adjustment Adjust by bending float arm at tab "A". Scheme 85

FLOAT DROP

Remove air horn gasket, position air horn right-side up, and let float hang down by its own weight. Measure distance between bottom of float and air horn. Float drop measurement should be 1.89" (48 mm). Adjust clearance by bending float tab "B". (Scheme 86)

Float Drop Adjustment Adjust by bending float tab "B". Scheme 86

UNLOADER

Fully open primary throttle valve, insert angle gauge, and measure choke valve angle. Choke valve angle should measure 45°. Adjust by bending primary throttle arm. (Scheme 87)

Choke Unloader & Throttle Valve Adjustment. Scheme 87

THROTTLE VALVE OPENING

1. Invert carburetor and fully open throttle valves. Measure angle of primary and secondary throttle valves, using angle gauge.
2. Angle of throttle valves should measure 90°. Adjust by bending the respective throttle arm. (Scheme 87)

SECONDARY TOUCH ANGLE

Measure the primary throttle valve angle as secondary throttle valve just begins to open. Primary throttle angle should measure 59°.

Bench Adjustment

Set throttle lever to high (first) step of fast idle cam. Fully close choke valve, insert angle gauge, and adjust primary throttle valve angle by turning fast idle adjusting screw. Angle adjustment is 23°.

CHOKE BREAKER

Apply vacuum to choke breaker diaphragm. Close choke valve by hand, insert angle gauge, and measure choke valve angle. (Scheme 88) Choke valve angle should measure 42°. Adjust by bending relief lever.

Choke Breaker Adjustment Adjust by bending relief lever. Scheme 88

CHOKE OPENER

1. Apply vacuum to choke opener diaphragm. Check that fast idle cam is released to fourth step. If not, adjust by bending choke opener lever.
2. Close choke valve, and set fast idle lever to first step. Ensure there is clearance between choke opener lever and fast idle cam.

IDLE-UP (THROTTLE POSITIONER)

Apply vacuum to idle-up diaphragm, insert angle gauge, and measure throttle valve opening. Adjust throttle valve opening angle to 16.5° by turning adjusting screw.

Scheme 89

1. Hold throttle slightly open, and push choke valve closed. Hold it closed as throttle valve is released.
2. Lever "A" should be holding lever "B" locked. (Scheme 89) Lever "A" should move smoothly at step 2 or 3 of fast idle cam. Adjust by bending top of lever "A". (Scheme 89): Adjusting Secondary Throttle Valve Lock System
3. While holding throttle slightly open and choke valve closed, rotate lever "B" until it makes contact with lever "A". Measure clearance between secondary valve and bore. Check for a maximum clearance of.020" (.5 mm).
4. With choke valve opened above 52°, check that lever "A" unlocks when throttle valve is opened. Repeat step 1). Apply vacuum to choke opener and check that lever "A" withdraws and that lever "B" unlocks.

DISASSEMBLY

Note. Manufacturer recommends using carburetor service kit 09860-11011 to disassemble and reassemble carburetor.

Air Horn

1. Remove metering needle, and disconnect fast idle link and air valve connecting rod. Remove the 5 air horn screws, and lift air horn from body. Remove air horn gasket.
2. Remove float pivot pin and float with the needle valve. Remove needle valve seat. Loosen power piston retaining screw. Hold piston, and rotate retainer. Remove piston and spring. Loosen the 3 screws, and remove the outer vent control valve.

Main Body

1. Remove slow jet using Jet Wrench (SST 09922-00010). Remove power valve with jets, metering needle guides, and secondary main jets.
2. Remove plug and primary main jets. Remove solenoid valve from body. Remove main and auxiliary acceleration pump housings, springs, and diaphragms.
3. Disconnect idle-up diaphragm link and diaphragm. Disconnect choke opener link, and remove choke opener. Remove 3 body-to-flange screws and remove flange from body.

CLEANING

Note. Do not immerse diaphragm valves, electrical components, or synthetic parts in carburetor cleaner.

Clean cast parts in carburetor cleaner and blow dry. Do not clean jets or other passages with wire or similar metal objects. Inspect all parts for wear or damage and replace necessary parts.

Choke Heater

Measure choke heater resistance between terminal and housing. Resistance should measure 20-22 ohms.

Choke Breaker, Choke Opener & Idle-Up Diaphragm

Apply vacuum to diaphragm and check for leakage. Ensure link or valve moves as vacuum is applied.

Float & Needle Valve

Inspect pivot pin for scratches and wear. Check float for wear in pivot pin holes and for broken lips. Inspect needle valve and seat for wear and damage and strainer for rust or breaks.

Primary Fuel Cut Solenoid

Connect battery voltage to solenoid terminals and feel solenoid for "click" as power is connected and disconnected. Inspect "O" ring for damage.

Power Piston

Inspect power piston and piston bore for wear and damage. Check spring for distortion or breaks.

Vent Control Valve

1. Check valve and seats for damage. Check that valve rod moves smoothly. Connect valve terminal wire to battery positive post. Jumper valve body to battery negative post.
2. A click should be felt from the control valve each time the valve wire is connected and disconnected to the battery positive post.

REASSEMBLY

Reassemble carburetor by reversing disassembly procedure, using new gaskets where required. Check for smooth operation of all valves and linkage.

Exploded View of Carburetor. Scheme 90

ADJUSTMENT SPECIFICATIONS

CARBURETOR ADJUSTMENT SPECIFICATIONS