Kymco MO BW250 Service Manual - chap13 (alimentazione)
13. FUEL SYSTEM/CARBURETOR/
FUEL PUMP/ FUEL TANK
13-0
Bet & Win 2 50
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FUEL SYSTEM/CARBURETOR/FUEL PUMP
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FUEL SYSTEM --------------------------------------------------------- 13- 1
SCHEMATIC DRAWING ---------------------------------------------- 13- 2
OPERATION OF CARBURETOR JETS------------------------------ 13- 3
SERVICE INFORMATION -------------------------------------------- 13- 5
CARBURETOR REMOVAL ------------------------------------------- 13- 7
VACUUM CHAMBER DISASSEMBLY------------------------------ 13- 7
FLOAT CHAMBER DISASSEMBLY--------------------------------- 13- 9
AUTO BYSTARTER INSPECTION/REMOVAL-------------------- 13-11
AIR CUT-OFF VALVE (A.C.V.)-------------------------------------- 13-12
AUTO BYSTARTER INSTALLATION ------------------------------ 13-14
FLOAT CHAMBER ASSEMBLY ------------------------------------- 13-15
FLOAT LEVEL INSPECTION ---------------------------------------- 13-16
VACUUM CHAMBER ASSEMBLY ---------------------------------- 13-16
CARBURETOR INSTALLATION ------------------------------------ 13-17
FUEL PUMP REMOVAL/DISASSEMBLY -------------------------- 13-18
FUEL PUMP INSPECTION-------------------------------------------- 13-19
FUEL PUMP ASSEMBLY --------------------------------------------- 13-19
FUEL PUMP INSTALLATION --------------------------------------- 13-20
FUEL TANK REMOVAL ---------------------------------------------- 13-20
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13. FUEL SYSTEM/CARBURETOR/
FUEL PUMP/ FUEL TANK
13-1
Bet & Win 2 50
FUEL SYSTEM
13. FUEL SYSTEM/CARBURETOR/
FUEL PUMP/ FUEL TANK
13-2
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SCHEMATIC DRAWING
13. FUEL SYSTEM/CARBURETOR/
FUEL PUMP/ FUEL TANK
13-3
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OPERATION OF CARBURETOR JETS
1. LOW SPEED
Venturi (slightly opened throttle valve)
Low Speed Air Inlet
※ Fuel in Float Chamber‡ Slow Jet
-------------------- Low Speed Small Jet Holes
2.MIDDLE SPEED
Venturi (halfway opened throttle valve)
High Speed Air Jet
※ Fuel in Float Chamber‡ Main Jet
Main Jet (The slow jet also works.)
Low & Middle Speed Supplementary Device:
Vacuum Tube
Low Speed Air Jet
Main Jet
Vacuum Diaphragm
Throttle
Valve
Low & Middle Speed Supplementary Fuel Inlets
Slow Jet
Bypass Jet
Pilot Screw
ACV
Air
※ Air
※ Air
Air Bleed Holes‡ Mixture…….
Air Bleed Holes‡ Mixture…….
13. FUEL SYSTEM/CARBURETOR/
FUEL PUMP/ FUEL TANK
13-4
Bet & Win 2 50
FUEL PUMP
CONSTRUCTION:
The fuel pump adopted for this model is a vacuum-type fuel pump which utilizes the positive and
negative pulsating pressures produced by the engine crankcase to control the oil pump diaphragms
and deliver fuel from the fuel tank to the carburetor through the suction valve and outlet valve.
FUEL PUMP CONSTRUCTION
Diaphragms
Inlet
Outlet
Suction Valve
Outlet Valve
Pulsating Pressure
from Crankcase
13. FUEL SYSTEM/CARBURETOR/
FUEL PUMP/ FUEL TANK
13-5
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SERVICE INFORMATION
GENERAL INSTRUCTIONS
• When working with gasoline, keep away from sparks and flames.
• Note the locations of O-rings when disassembling and replace them with new ones during
assembly.
• Before float chamber disassembly, drain the residual gasoline from the float chamber.
• Do not try to disassemble the auto bystarter.
• When assembling the vacuum chamber and air cut-off valve, be careful not to damage the
diaphragms.
• All cables, fuel lines and wires must be routed and secured at correct locations.
• When removing the fuel tank, keep sparks and flames away from the working area.
• When removing the fuel tank, the remaining fuel in the tank must be lower than _ of the fuel tank
capacity to avoid gasoline overflowing.
• Fuel tank capacity: 10.5 liters
SPECIFICATIONS
SH50CA
Venturi dia. (mm)
CVK30
Identification number
CVK038B
Float level (mm)
18.5
Pilot screw opening
1/2~4
Main jet
108#
Slow jet
38#
Idle speed
1450
Fuel pump output
17L/Hr/7000rpm
SPECIAL TOOLS
Float level gauge
Fuel unit remover
13. FUEL SYSTEM/CARBURETOR/
FUEL PUMP/ FUEL TANK
13-6
Bet & Win 2 50
TROUBLESHOOTING
Engine does not start Engine idles roughly, stalls or runs poorly
• No fuel in tank • Incorrect idle speed
• Restricted fuel line • Rich mixture
• Too much fuel getting to cylinder • Lean mixture
• Clogged air cleaner • Clogged air cleaner
• Contaminated fuel • Intake air leak
• Faulty fuel pump • Contaminated fuel
• Faulty air-cut off valve
• Damaged vacuum tube and connectors
• Damaged carburetor insulator
Throttle does not open fully, so engine stalls Rich mixture
• Damaged vacuum piston diaphragm • Auto bystarter valve opens excessively
• Clogged diaphragm hole • Faulty float valve
• Float level too high
Lean mixture • Clogged air jets
• Clogged fuel jets • Auto bystarter valve set plate installed in
• Clogged fuel tank cap breather hole
the wrong groove
• Clogged fuel filter •Clogged air cleaner
• Bent, kinked or restricted fuel line
• Faulty float valve
• Float level too low
• Faulty fuel pump or insufficient output
Engine is hard to start
• No fuel in tank
• Restricted fuel line
• Clogged fuel strainer
• Faulty fuel pump
• Broken or clogged vacuum tube
• Faulty or clogged charcoal canister
Lean mixture
• Clogged charcoal canister
• Bent, kinked or restricted fuel line
• Clogged fuel strainer
• Float level too low
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