4. Honda CB 750 K7 - FUEL SYSTEM

~ HONDA 4. FUEL SYSTEM
~ CB750

I

~1

()~ !

~~

~

~

~

4-0

FUEL SYSTEM ~ HONDA

TROUBLESHOOTING ~ CB750

SERVICE INFORMATION 4-1
4-3
FUEL TANK 4-4
4-5
CARBURETORREMOVAL 4-6
4-10
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

4-1

(;if\ HONDA FUEL SYSTEM

~ CB750

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 07401-0010000

FLOAT GAUGE

SPECIFICATIONS

Fue l 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 SYSTEM

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. (1) FUEL FILTER
Work in a well-ventilated area. (2) FUEL COCK
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.

4-4

-

~ HONDA FUEL SYSTEM

~ 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.

r
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.

-4-5

FUEL SYSTEM a HONDA

~ CB750

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 (l)LINK FIXING SCREW
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.

4-6

~HONDA FUEL SYSTEM

~ CB750

r

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. (2)THROTTLE VAL VE

Loosen the two screws and remove the
throttl~ valve and jet needle from the link
arm.

~r

(3)JET NEEDLE ~

,--... N0.3 CARBURETOR DISAS- (1) PIN REMOVER and DRIVER 07944-0980000
- 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.

4-7

FUEL SYSTEM ~ HONDA

~ CB750

ACCELERATOR PUMP REMOVAL

Remove the accelerator pump from the No.
2 carburetor by unscrewing the three
screws.

FLOAT/MAIN JET/PILOT SCREW (8) FLOAT PIN
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.

4-8

~ HONDA FUEL SYSTEM

~ CB750 (1) PI LOT SCREW (2)NEEDLE JET

Inspect the pilot screw, jet needle, needle ~
jet and float valve for hardened deposits,
grooving, or other damage and replace if
necessary.

(4) FLOATVALVE

- - - - (3) JET NEEDLE

Inspect the main and slow jets for clogging,
and blow with a compressed air if
necessary.

-;;:: ~

LINK ARM INSTALLATION ( !)THROTTLE VALVE CUTWAY

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.

4-9

FUEL SYSTEM ~HONDA

CARBURETOR ~ CB750
ASSEMBLY
( l )LINK ARM F OR
NO. 2 CARBURETOR ASSEMBLY N0 .2 CARBURE T OR

The link arm which is not equipped with an
adjusting screw should be installed in the
No. 2 carburetor.

(2)LINK ARM F OR
N0. 1. 3 AN D 4 CARBURETOR

Install the choke shaft levers and springs
properly.

Fuel Line

4-10

~HONDA FUEL SYSTEM

~ CB750 (1) CHOKE SHAFT
(2) CHOKE VALVE
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.)

(1) FLOAT LEVEL

4-11

FUEL SYSTEM ~ HONDA

0-0.2 mm ~cc!=~===!~ ~ CB750
(0-0.008 in.)
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 bend-
ing 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 (0.374-0.413in.)

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· D

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 re-
moval.

NOTE
Do not reverse the OPEN and CLOSE
L CABLES.

After installing the carburetors, perform
the following operations:
Throttle cable adjustment
Choke cable adjustment
Carburetor synchronization
Idle speed adjustment

4-12