Carburetor - Mikuni 2-bbl Hyundai Excel I

DESCRIPTION

Mikuni 28-32 DIDEF carburetor is used on the Excel. These 2-barrel, 2-stage carburetors use primary and secondary circuits. Carburetor components include conventional accelerator pump, vacuum-actuated secondary throttle diaphragm, sub-EGR valve system, fully automatic choke, coasting air valve, fuel cut-off solenoid anti-overfill device, air switching valve, bowl vent valve and dashpot.

MIKUNI CARBURETOR IDENTIFICATION

Note. Some 1987 vehicles have been retrofitted with 1988 carburetors. See NEW CARB SYSTEM article in TSB/RECALLS/TECH TIPS section.

ADJUSTMENTS

Note. For all on-vehicle adjustments not covered in this article, see TUNE-UP - 4-CYL article in ENGINE PERFORMANCE section.

FACTORY ONLY

The automatic choke, choke breaker (vacuum kick), fast idle, secondary throttle opener, accelerator pump and sub-EGR valve have all been factory-calibrated. Do not change any of these adjustments for any reason.

Scheme 20

1. Invert float chamber cover assembly without gasket. Using a universal float level gauge, measure distance from bottom of float to surface of float chamber cover. Distance should be.748-.826" (19-21 mm). (Scheme 20)
2. If float level is not within specified range, adjust by increasing or decreasing the number or thickness of needle valve shims. Adding or subtracting a shim will change fuel level about 3 times the thickness of the shim.
3. Adding shims lowers float level. Shims are available in a set of 3 thicknesses:.012" (0.3 mm),.016" (0.4 mm) and.020" (0.5 mm).
4. To install shim, remove the float, needle and needle seat. Check filter for clogging or damage. Install new "O" ring to needle seat. Install shim and filter to needle seat. (Scheme 21) Install assembly into float chamber cover.
5. Install seat retainer. Tighten screws firmly. Insert needle into seat. Install float. Recheck float level using procedure in step 1).

Scheme 21

ACCELERATOR CABLE

1. With engine at normal operating temperature, adjust accelerator cable. Loosen lock nut and adjusting nut. Remove any sharp bends from cable.
2. Turn adjusting nut to a point where throttle lever just starts to move. Then back nut off 1/2 turn. Secure with lock nut. (Scheme 22) After adjustment, operate accelerator pedal to ensure throttle valve operates smoothly from fully closed to fully opened position.

Scheme 22

Scheme 23

DISASSEMBLY

Note. DO NOT invert carburetor during disassembly. Do not remove choke valves, choke levers and related parts, round nut from accelerator pump link, adjusting screws (except idle speed, idle mixture and dashpot), or throttle valves.

Scheme 24

1. Disconnect water hose from throttle body and choke chamber. Grind heads off choke cover lock screws. Remove cover. Disconnect ground wire from fuel cut-off solenoid at cover assembly (if equipped).
2. Remove throttle return and damper springs. Remove vacuum hose from depression chamber and throttle body. Remove accelerator pump rod from throttle lever.
3. Remove dashpot/idle up actuator rod (man. trans.) or idle up actuator rod (auto. trans.) from free lever. On Pickup and Ram-50 models, remove dashpot rod from free lever. Remove actuator.
4. Remove the deceleration, enrichment and jet mixture solenoid valves. On all models, remove depression chamber rod from secondary throttle lever. Remove the depression chamber. (Scheme 24)
5. Remove 2 long float chamber cover screws. Remove throttle body. Remove 4 short screws, and float chamber cover from main body. Remove check weight and ball, and steel ball of anti-overfill device.
6. Remove float pin and float. Remove screw, retainer and needle valve.
7. Remove main jets from jet blocks. Using a screwdriver, remove pilot jet retainer and pilot jet. Remove accelerator pump mounting screws, pump cover and link assembly, diaphragm, spring, body and gasket from main body.
8. Remove snap ring from sub-EGR control valve pin. Remove pin and link from valve. Remove small steel ball and spring from sub-EGR control valve. Remove sub-EGR valve from throttle body.

CLEANING & INSPECTION

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

1. Clean all parts with soft brush and solvent. Check throttle valve and choke valve shafts for proper operation. If not operating properly, clean and lubricate.
2. Check jets for damage or clogging. Clean with compressed air. Never use wire or other metal objects. Check idle mixture adjusting screw for grooves, ridges or other damage.
3. Check needle valve assembly, strainer screen and vacuum chamber. Check fuel cut-off solenoid operation using battery voltage. Needle should move in when solenoid is attached to battery. Needle should move out when disconnected.
4. Thoroughly inspect carburetor main body, throttle body and float chamber cover for cracks or other damage. Apply vacuum to diaphragms. Check for leakage.

REASSEMBLY

1. To reassemble, reverse disassembly procedure. Ensure that all air and fuel passages are clear. Lubricate linkage after cleaning. Check throttle and choke linkage for smooth operation.
2. Be sure that sub-EGR valve is operating smoothly. If a main or pilot jet needs to be replaced, make sure that replacement jet is of the same size. A number is stamped on each jet.
3. To prevent carburetor-to-intake manifold gasket from being installed incorrectly, match holes of gasket to throttle body. Place gasket on intake manifold.

Note. For specifications, see ADJUSTMENTS in this article.