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~ HONDA ~ CB750
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4. FUEL SYSTEM
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4-0
FUEL SYSTEM
TROUBLESHOOTING
SERVICE INFORMATION
FUEL TANK
CARBURETORREMOVAL
CARBURETOR DISASSEMBLY
CARBURETORASSEMBLY
TROUBLESHOOTING Engine Cranks But Won't Start
1. No fuel in tank 2. No fuel to cylinders 3. Too much fuel to cylinders 4. No spark at plugs (ignition malfunct ion) 5. Air clearner clogged
Engine Idles Roughly, Stalls, or Runs Poorly
1. Idle speed incorrect 2. Ignition malfuction 3. Low compression 4. Rich mixture 5. Lean mixture 6. Air cleaner clogged 7. Air leaking into mainfold 8. Fuel contaminated 9. Carburetors not synchronized
Lean Mixture
1. Carburetor fuel jets clogged 2. Vacuum piston stuck closed 3. Fuel cap vent blocked 4. Fuel filter clogged 5. Fuel line kinked or restricted 6. Float valve at fault 7. Float level too low
Rich Mixture
1. Choke stuck closed 2. Float valve defective 3. Float level too high 4. Carburetor air jets clogged
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(;if\ HONDA ~ CB750 FUEL SYSTEM
SERVICE INFORMATION WORKING PRACTICE
Use caution when working with gasoline. Always work in a well-ventilated area and away from sparks or open flames. When disassembling fuel system parts, note the locations of the 0-rings. Replace them with new ones on re-assembly. The float bowls have drain plugs that can be removed to drain residual gasoline.
SPECIAL TOOL
FLOAT GAUGE
SPECIFICATIONS
07401-0010000
Fuel Low-lead gasoline with 91 octane number or higher Fuel tank F-Model: 17.5 lit. (4.8 U.S. gal., 3.9 Imp. gal.) K-Model: 19.5 lit. (5.1 U.S. gal., 4.3 Imp. gal.)
Carburetor type : 4, piston valve type Venturi dia. : 28 mm
Setting K7 F2
Setting mark PD41A PD41B
Main jet # 115 # 105
Slow jet # 35 # 35
Main air jet # 150 # 120
Slow air jet # 150 # 150
Jet needle setting F2051E-1 F2051F-2
Pilot screw opening 1½ 1¾
Float level 12.5 mm (0.4921 in.) 14.5 mm (0.5709 in.)
Idle speed 1,000± 100 rpm 1,000 ± 100 rpm
4-3
FUEL TANK Turn the fuel valve "OFF"
Remove the fuel lines from the fuel valve . . Replace the fuel line with a new one if cracked or deteriorated.
Place a pan under the fuel valve and turn the fuel valve "ON" or "RES", and inspect the fuel strainer screen and the filler cap vent hole for clogging.
Keep away from sparks or open flames. Work in a well-ventilated area. Keep gasoline in a safe place.
If the fuel strainer screen is clogged, drain fuel from the fuel tank.
Unscrew the fuel valve lock nut and remove the fuel strainer screen and packing.
Clean or replace the fuel strainer screen if necessary.
Wash the inside of the fuel tank with solvent, if there is water or any other foreign matter in the fuel.
Install the fuel strainer screen packing and fuel valve.
NOTE
Do not overtighten the fuel valve lock nut.
After assembling, fill the tank with fuel and check for leaks.
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FUEL SYSTEM
(1) FUEL FILTER
(2) FUEL COCK
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~ HONDA ~ CB750
CARBURETOR REMOVAL Turn the fuel valve "OFF" and disconnect the fuel line at the fuel valve.
Open the seat and remove the fuel tank.
Remove the air cleaner lower case by loosening the two mounting bolts.
Loosen the air cleaner connecting bands and remove the two air cleaner hanger bolts.
Remove the air cleaner upper case from the carburetors.
Remove the throttle and choke cables from the cable holder and disconnect them from the choke shaft levers.
Loosen the carburetor insulator bands and take the carburetor assembly out.
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FUEL SYSTEM
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CARBURETOR DISASSEMBLY Remove the carburetor assembly from the engine.
Remove the choke valve from the choke shaft by removing the two screws. Remove the accelerator pump fuel tubes.
Remove the carburetor top by loosening the two screws.
Loosen the link arm fixing screw. Loosen the lock nut and remove the throttle lever set screw.
Remove the rear stay from the carburetor assembly by loosening the four bolts.
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FUEL SYSTEM
(l)LINK FIXING SCREW
a HONDA ~ CB750
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~HONDA ~ CB750
Remove the throttle return spring from the stopper arm.
Remove the stay plate by loosening the eight screws. Remove the accelerator pump spring.
Unhook the choke relief spring at the choke lever.
Separate the carburetors.
Remove the link arm from the carburetor.
Loosen the two screws and remove the throttl~ valve and jet needle from the link arm.
,--... N0.3 CARBURETOR DISAS-- SEMBLY
(THROTTLE STOPPER REMOVAL)
Place the throttle link on suitable supports or blocks.
CAUTION
Use care when driving out to give light, careful hammer blows to the drift.
FUEL SYSTEM
(2)THROTTLE VAL VE
~r (3)JET NEEDLE ~
(1) PIN REMOVER and DRIVER 07944-0980000
4-7
ACCELERATOR PUMP REMOVAL
Remove the accelerator pump from the No. 2 carburetor by unscrewing the three screws.
FLOAT/MAIN JET/PILOT SCREW REMOVAL
Remove the carburetor assembly from the engine.
Remove the float chamber from the carburetor by loosening the three screws.
Pull the float arm pin out and remove the float.
Remove the main jet.
NOTE The slow jet must not be removed since it is a tight pressure fit.
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FUEL SYSTEM
~ HONDA ~ CB750
(8) FLOAT PIN
~ HONDA ~ CB750
Inspect the pilot screw, jet needle, needle jet and float valve for hardened deposits, grooving, or other damage and replace if necessary.
Inspect the main and slow jets for clogging, and blow with a compressed air if necessary.
LINK ARM INSTALLATION
To assemble the carburetors, reverse the foregoing disassembly procedure.
Observe the following notes:
Connect the throttle valve to the link arm so that the cutaway is facing the choke valve.
FUEL SYSTEM
(1) PI LOT SCREW (2)NEEDLE JET
~ (4) FLOATVALVE
---- (3) JET NEEDLE
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( !)THROTTLE VALVE CUTWAY
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CARBURETOR ASSEMBLY NO. 2 CARBURETOR ASSEMBLY
The link arm which is not equipped with an adjusting screw should be installed in the No. 2 carburetor.
Install the choke shaft levers and springs properly.
Fuel Line
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FUEL SYSTEM
~HONDA ~ CB750
( l )LINK ARM F OR N0.2 CARBURE T OR
(2)LINK ARM F OR N0. 1. 3 AN D 4 CARBURETOR
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~HONDA ~ CB750
Install the choke plate to the choke shaft by using the lock washer and screws.
NOTE
Check that the choke link moves freely and bend the lock washer up against the screw heads. Do not reuse the choke valve screws as they were peened at the factory.
FLOAT LEVEL
Measure the float level.
NOTE Measure the level where the float arm just contacts the float valve when the valve is closed.
If necessary, adjust the float level by bending the float arm carefully.
FLOAT LEVEL : "F" model 14.5 mm (0.5709 in.) "K" model 12.5 mm (0.4921 In.)
FUEL SYSTEM
(1) CHOKE SHAFT
(2) CHOKE VALVE
(1) FLOAT LEVEL
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ACCELERATOR PUMP ADJUSTMENT
Remove the carburetor assembly from the engine.
Measure the pump rod-to-pump arm clear· ance with the throttle valve closed.
If necessary, adjust the clearance by bending the pump arm.
CLEARANCE: 0-0.2 mm (0-0.008 In )
Measure the pump arm-to-carburetor stay clearance with the throttle valve closed.
If necessary, adjust the clearance by bending the pump arm.
CLEARANCE: 9.5-10.5 mm (0.37 4-0.413in.)
FASTIDLE
Pull the choke link arm up fully and turn the adjusting screw until it lightly seats the stopper.
Return the choke link arm and turn the ad· sting screw 2½ turns in.
After installing the carburetor, check the fast idle sped.
FAST IDLE SPEED: 2750 ± 750 rpm
CARBURETOR INSTALLATION Installation is the reverse order of the removal.
NOTE
Do not reverse the OPEN and CLOSE LCABLES.
After installing the carburetors, perform the following operations:
Throttle cable adjustment Choke cable adjustment Carburetor synchronization Idle speed adjustment
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FUEL SYSTEM
0-0.2 mm ~cc!=~===!~ ( 0-0.008 in.)
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~ HONDA ~ CB750
