Cobra Moto 2008 X50JR User manual

For parts orders contact your local dealer
To locate your closest Cobra dealer
log on to
www.cobramotorcycle.com
or call
[phone]
If you need technical assistance
contact your local dealer or call
the Cobra Technical Support Hotline at
[phone]
Cobra Motorcycle MFG., Inc.
240 Uran Street
Hillsdale, Michigan 49242

DISCLAIMER OF WARRANTY
This motorcycle is sold “as is” with all faults, obvious or not. There are no warranties
expressed or implied, including any warranty of merchantability and warranty of fitness
for any particular purpose.
“WARNING”
THE COBRA CX50JR IS A COMPETITION MODEL ONLY AND IS NOT
MANUFACTURED FOR, NOR SHOULD IT BE USED ON PUBLIC STREETS, ROADS
OR HIGHWAYS.
THE USE OF THIS BIKE SHOULD BE LIMITED TO PARTICIPATION IN
SANCTIONED COMPETITION EVENTS UPON A CLOSED COURSE BY A
SUFFICIENTLY SKILLED RIDER AND SHOULD NOT BE USED FOR GENERAL
OFF-ROAD RECREATIONAL RIDING.
IMPROPER USE OF THIS MOTORCYCLE CAN CAUSE INJURY OR DEATH.
THIS BIKE IS INTENDED FOR EXPERIENCED RACERS ONLY AND NOT FOR
BEGINNERS.
IT IS YOUR RESPONSIBILITY AS THE OWNER OF THIS COBRA MOTORCYCLE
OR AS THE PARENT, OR LEGAL GUARDIAN OF THE OPERATOR, TO KEEP THIS
COBRA MOTORCYCLE IN PROPER OPERATING CONDITION.
THIS BIKE WAS DESIGNED FOR RIDERS THAT WEIGH LESS THAN 80 LBS WITH
FULL RIDING GEAR AND SHOULD NOT BE OPERATED BY RIDERS THAT WEIGH
MORE THAN THAT.
BE SURE THAT THE RIDER ALWAYS WEARS ADEQUATE SAFETY GEAR
EVERYTIME HE OR SHE RIDES THEIR COBRA MOTORCYCLE.
IMPORTANT SAFETY NOTICE
Failure to follow WARNING instructions could result in severe injury or death to
the machine operator, a bystander, or a person inspecting or repairing the
machine.
CAUTION:
A CAUTION indicates special precautions that must be taken to avoid damage to
the machine.
NOTE:
A NOTE provides key information to make procedures easier or clearer.
MCCJ2008.6

Table Of Contents
General Information..............................................................................................5
Specifications - General....................................................................................5
Specifications - Torque Values..........................................................................6
Optional Components........................................................................................7
Break-In Procedure...........................................................................................8
Starting Procedure ............................................................................................9
Maintenance .......................................................................................................10
Tips .................................................................................................................10
Schedule .........................................................................................................11
Replacing Transmission / Clutch Lubricant .....................................................12
Proper Chain adjustment.................................................................................14
Air Filter Cleaning............................................................................................14
Fork Oil Replacement......................................................................................16
Frictional Drive (CFD)......................................................................................17
Parts ...................................................................................................................18
Parts – Airbox and Inlet System......................................................................18
Parts – Bars and Controls ...............................................................................19
Parts - Carburetor............................................................................................20
Parts - Carburetor............................................................................................20
Parts – Coolant System...................................................................................21
Parts – Electrical System ................................................................................22
Parts – Engine – Bottom End and Transmission............................................23
Parts – Engine Clutch and Kicker................................................................24
Parts – Engine – Water Pump .....................................................................25
Parts – Engine – Top End............................................................................26
Parts – Exhaust System..................................................................................27
Parts – Forks & Triple Clamps.........................................................................28
Parts – Forks – Leg Assembly.....................................................................29
Parts – Frame – Mounting Hardware I ............................................................30
Parts – Frame – Mounting Hardware II........................................................31
Parts - Frame – Mounting Hardware III........................................................32
3

Parts – Front Brakes .......................................................................................33
Parts – Front Wheel ........................................................................................34
Parts – Plastic Bodywork & Seat.....................................................................35
Parts – Rear Brake..........................................................................................36
Parts – Rear Wheel.........................................................................................37
Parts – Shock..................................................................................................38
Parts – Swingarm Assembly............................................................................39
Service................................................................................................................40
Engine Service................................................................................................40
Base Gasket Selection ................................................................................41
Engine Removal ..........................................................................................43
Complete Engine Disassembly Procedure ..................................................44
Top End Disassembly Procedure ................................................................44
Splitting the Cases.......................................................................................45
Engine assembly .........................................................................................46
Clutch..............................................................................................................48
Ignition.............................................................................................................53
Cooling System...............................................................................................55
Fuel & Air System............................................................................................59
Exhaust ...........................................................................................................62
Wheels & Tires................................................................................................63
Tuning.................................................................................................................63
Suspension .....................................................................................................63
Rear shock...................................................................................................65
Front Forks ..................................................................................................65
Gearing ...........................................................................................................66
Carburetion .....................................................................................................68
Troubleshooting..................................................................................................70
Index...................................................................................................................72
4

General Information
Specifications - General
Items CX50 JR
Dimensions
Wheelbase 35.75” (908mm)
Wheel size 10” (254mm)
Seat height 23.9” (607 mm)
Engine
Type 2-stroke, single cylinder, reed valve
Cooling system Liquid-cooled
Coolant Liquid Performance Mini Coolant or Antifreeze
Displacement 49.8 cc
Bore and stroke 39 mm x 41.7 mm, “V” head
Ignition system Electronic, analogic advance
Spark plug Champion 8339-1, 8332-1 hotter, 8904-1 colder
Gap 0.023” – 0.025” (0.58 – 0.64 mm)
Ignition timing 0.040” (1.0 mm) Before Top Dead Center (BTDC)
Fuel type High octane pump gasoline
RACE FUELS ARE NOT RECOMMENDED
Oil type Cobra Venom 2-cycle Race Oil
Fuel / oil mix ratios Between 32:1 and 40:1 (after engine Break-In)
Carburetion 14 mm Dell’Orto
Main Jet 92
Slow (Pilot) jet 55
Float Height 16mm +0.5mm (0.63” +0.020”)
Transmission
Speed / Clutch Single / Cobra 3 shoe
Final drive ratio 13/37T or 14/38 T
Chain 420
Transmission / clutch oil type Cobra Venom 3 Shoe Clutch Milk
Quantity 235 – 350 ml (8 – 12oz)
5

Chassis
Front tire 2.50 – 10
Pressure 15 psi minimum
Rear tire 2.75 – 10
Pressure 15 psi min. (20 psi for hard pack or rocky conditions)
Front fork Marzocchi 32mm
Fork oil type SAE 20 weight
Fork oil amount 200 ml (6.8 oz) oil change, 220 ml (7.4 oz) rebuild
Collapsed fork oil height 70 mm (2.75”) spring in, no spacer
Specifications - Torque Values
Torque Value
Fastener ft-lb in-lb Nm
Size &
Remarks
Cylinder head nuts 8.8 105 12 M6 X 1.0
Crankcase bolts 8.8 105 12 M6 x 1.0
Spark plug (SP) (SP) (SP) M14 x 1.25
Stator bolts 2.1 25 2.8 M5 X 0.8
Stator cover bolts 1.7 20 2.3 M4 X 0.75
Clutch cover bolts 5.8 70 7.9 M6 X 1.0
Clutch nut (max.) 40 480 54 10 x 1.25*
Clutch bolts 12 144 16 M6 x 1.0
CFD nut 55 664 75 ½” x 20 LHT
Engine mount bolts 22 265 30 M8 X 1.25
Swingarm Pivot 21 250 28 M14 X 2.0
Shock Bolt 35 420 47 M10 x 1.5**
Water Pump
Impeller 3.6 44 5 M5 x 0.8*
Intake manifold bolts 4.6 55 6.2 M6 X 1.0
Ignition rotor nut 40 480 54 M10 x 1.25*
6

Rear Sprocket Bolts 18 216 24 M7 X 1.0**
Axle nuts 25 300 34 M12 X 1.25
* Apply high strength thread locking agent when installing
**Apply medium strength thread locking agent when installing
(SP) To apply the proper torque to the spark plug when inserting, one must first
screw the spark plug in until the metal gasket ring causes resistance and then
turn another 1/8 to ¼ turn.
Optional Components
Call your dealer, or the factory, for details
• Carburetor jets
• Pre-filter for the airbox
• Sprockets
o Front
o Rear
• Suspension Springs
Weight of Rider (lb) Fork Spring Shock Spring
Less than 38 (light) KCMZ0012A
(12 lb/in, 2.10 N/mm))
SCMUOH04
(275 lb/in) red
38 – 45 (std) KCMZ0012
(14 lb/in, 2.45 N/mm))
SCMUOH05
(285 lb/in) yellow
46 to 55 (stiff) KCMZ0012B
(16 lb/in, 2.80 N/mm)
SCMU0H06
(295 lb/in) white
• Suspension valving
Damping Rate Fork Valving
Compression
(right)
Fork Valving
Rebound
(left)
Shock Valving
(kit)
Soft (fast) KCMZ0033A KCMZ0032A SCMUOH07
Standard KCMZ0033 KCMZ0032 SCMUOH08
Hard (slow) KCMZ0033B KCMZ0032B SCMUOH09
• Tires
• Tubes or ‘Tire Balls’
7

Break-In Procedure
Your Cobra CX50 JR is a close-tolerance high performance machine and break-
in time is very important for maximum life and performance. The CX50 JR can be
ridden hard after the first ½ hour break-in time but it is recommended that no
adjustments are made to the carburetion or suspension until the full 8 hours of
bike break-in has elapsed. Also, after the engine, transmission, and drive train
have been broken-in for the full 8 hours, the bike will be faster!
Use a fuel / oil mixture of 32:1 for the full 8 hour break-in period. Be sure to use
high octane pump gas with Cobra’s specially formulated Cobra Venom 2-cycle
Race Oil. (Part # MCMUOL02)
CAUTION:
Failure to use proper fuel, oil, or fuel/oil mixture may result in premature engine
wear or damage to the machine.
Adhering to the following break-in schedule will result in long lasting high
performance machine.
• Start bike on stand
• First 5 minute period, operate the bike on the stand with a combination of idle
and high RPM operation. (avoid prolonged high RPM but spin the rear
wheel good at least once or twice per minute)
• Allow bike to cool
• Ride for 15 minutes maximum (avoid prolonged high RPM operation and
avoid abusing the clutch with throttle blipping.
• Cool and inspect bike for loose fasteners.
• Next ½ hour of operation, avoid prolonged operation at Wide Open Throttle.
• After 1 hour of operation
o Check for loose bolts and nuts on the bike and retighten as
necessary (proper toque values are listed under Specifications).
o Clean the carburetor bowl.
o Change the transmission / clutch lubricant.
• After 8 hours of operation
o Change the fork oil.
o Have a Certified Cobra Mechanic change the shock oil.
• Your bike is now ready for the highest level of competition!
NOTE:
During break-in the bike will likely lose some engine coolant through the radiator
overflow hose. Losing up to 4 oz (120 ml, ½ cup) is normal. Proper coolant level
will cover the top of the radiator cores. Removing the radiator cap and looking
inside is the only way to check the coolant level.
8

Never open the radiator cap of a machine that has a hot or warm engine or one
that has recently been ridden. Burning and scalding could occur.
CAUTION:
It is important that the radiator cap is installed correctly and completely otherwise
engine damage could occur.
Starting Procedure
Before starting the machine inspect the following:
• Check for proper tire pressure in both tires.
• Observe the chain tension and adjust if necessary.
• Observe the coolant level and fill if necessary.
Verify that the chain rollers and sliders do not have improper wear.
• Verify that the handlebars are tight.
• Check the throttle for smooth operation and that it ‘clacks’ shut properly.
• Check for loose bolts and nuts, and re-torque as necessary.
• Verify that the air filter is clean and properly saturated with oil.
• Insure that the fuel tank contains an adequate volume of fuel / oil mixture to
complete the distance required. (High octane pump gas with Cobra’s
specially formulated Cobra Venom 2-cycle Race Oil)
• Turn the fuel on by rotating the fuel petcock knob to the vertically downward
position (reserve position is horizontally forward)
CAUTION:
For best results from your Cobra Motorcycle use only the recommended fuels.
Testing has shown that most ‘race’ fuels actually degrade performance.
Always wear a helmet and other protective riding gear.
When your pre-ride inspection is complete the bike may be started. For a cold
engine follow this procedure.
1. Place the motorcycle on a stand of sufficient strength that positions the
motorcycle in a level upright position with the rear wheel off the ground.
2. Pull up the choke knob and turn it to lock it.
3. Kick start the engine.
4. Rev the engine in short spurts, turning the throttle no more than 1/4 open
until the engine will run without the choke.
5. Verify a functional engine shut-off switch by shutting off the engine.
6. Restart the engine and proceed with riding when the engine is sufficiently
warm (i.e. the side of the cylinder is warm to touch).
9