Of the above bikes the Honda CBR125 is by far in the majority but there has been a few Yamahas and a sole KTM 125 Duke. In the right hands any bike can be competitive the the Honda CBRs are readily available and cheap to prepare and run.

There may be other Asian bikes out there which could be eligible, however for this article we will only concern ourselves with the Honda CBR125.

Sourcing a suitable Commuterlite

Look in the Auctions, Wreckers, Gumtree, Trading post and motorcycle sales sites on the web. Usually the Honda CBR125 can be picked up cheap with superficial crash damage.

Success

So you've managed to get your hands on a donor Honda CBR125. To turn your sporty road going bike into a competitive Commuterlite race bike You will need to do the following:

Race preparation

Race preparation must be done according to the MA's Road racing GCRs (General Competition Rules) which can be found in the  MOMs (Manual Of Motorcycle Sport). The manual is now published in it's entirety on the web and can be found HERE... on the MA's website.

Shopping List

Put the following on your shopping list:

• Tires; 110/80 x17 rear and 90/80 x17 front (Sava seems to be the tyre to have)
• After market sports exhaust.
• 2 x 6mm alloy plates to raise and move foot pegs to rear. (this is not essential but it does give more ground clearance and makes it easier to get into the racing crouch)
• Lock wire
• Roll of pvc tape.
• Race Numbers
• Race number background paint (BlacK)
  

For Recalibrating the Fuel Injection map.

• 1x 5K potentiometer
• a few 1/2 watt resistors
• 50mm clear sleeve or heat shrink to slip over resistor.

And that's it, it certainly won't break the bank

Engine

The engine must remain standard except for the modifications allowed in the rules, the CBR125 engine should be ultra reliable in this totally unmodified guise, hence keeping running costs down. The OEM ECU must be retained and rev limiter must remain as supplied.

The starter motor must remain along with the battery and standard alternator, all OEM. The bike must be able to start off of it's installed start motor at all times.

Exhaust

After market sports exhaust. a NMF pipe gave excellent results in the test bike prepared by Garry Briggs of Big Bang Engines and ridden by Stephen Kairl at Eastern Creek. Fuel Injection map will need to be recalibrated see below.
(Do not consider using the stock pipe with catalytic converter.) A good aftermarket exhaust has power and weight benefits.

Since this article was originally written other brand exhaust pipes such as Yoshimura, DBS, Endurance and homemade systems have enjoyed success.

Fuel Injection

• Fuel Injection must be retained, carbys not allowed if fuel injection is originally fitted.
  
• When a hi-performance exhaust is fitted the fuel map has to be recalibrated.

 

To recalibrate the fuel map:

• Find the plug (3 wires) for the water temp sensor on the thermostat housing. (Underneath the petrol tank on RHS looking forward) See picture below.
  
  
• Cut the Yellow/Blue wire and place a 0-5K potentiometer (available from Jaycar) in series. More resistance = more fuel. Should be done on a Dyno with an O2 sensor. Once the correct value has been established, replace the potentiometer with a 10c resistor of the closest standard value. When adjusting the potentiometer, the engine has to be off when changing the value from low to high, but you can change from high to low with it running.
   
• Resistor sizes in 1.2Kohm to 1.8Kohm range seems to work but it really needs to be put on a dyno to finalise the correct value. However anything around those values should get you started. Several bikes run well on a 1.4K resistor.

 

Wiring Electrical.

All electrical equipment not required on a race bike should be discarded.

Disconnect the battery before doing any electrical work.:

Discard

• Headlights, tail light, flasher lights and flasher unit.
• Horn, you wont be needing it on the track.
• It's ok with the rules to remove the radiator fan.
  
• sub sections of wiring loom not needed can go but be careful when disconnecting stuff as for instance when you remove the side stand and disconnect it's switch the bike wont start.
• As you progress through disconnecting things, reconnect the battery every other disconnection and check the bike still starts. That way you wont have far to backtrack to troubleshoot the problem.
  

The tilt switch has also caused some grief, if your bike doesn't start check that its in the right orientation. If it's upside down it sends a signal to the CPU that the bike is upside down and shouldn't be running.

Instrument Panel

The standard instrument panel is good to use does the job but its ok to use aftermarket gauges if it's damaged. Replacement cost of standard panel is prohibitive.

Airbox.

Originally it was recommended to remove the air filter and box  completely and leave the plastic air intake bellmouth on Fuel Injector body. Now it seems its better to leave the bottom half of air box in place along with the inlet bellmouth. Remove silencer box from plastic bellmouth and seal hole.

Fuel

No point in using exotic fuels, compression ratio too low.

Chassis Mods.

Tyres

Sticky tires. Sava 110/80 x17 rear and 90/80 x17 front seem to be a popular choice. They must be mounted on standard OEM rims. Get the tyre fitted by your seller and have the wheels balanced. Dunlop's, Pirellis and Bridgestone's have been used with varying success.

Forks

Cut 100mm off of tighter wound end of fork spring and fit with a 100mm packing piece cut from suitable sized tubing (22mm Outside Diameter, aluminium or steel) Use a suitable size washer between spring and tube.

Rear Suspension

Rear suspension unit can be modified/changed but is fine if it's in good condition. The adjustable YSS and Elka shocks made for the CBR125 may offer some improvement but are expensive.

Rear set Footpegs

Footpegs can be left as is but they are low and can ground. Two alloy plates as per the picture below can be run up and do the job nicely getting the footrests up and back. Aftermarket footrests are available from Thailand but again bumps the cost up.

Rear sub-frame.

To facilitate the fitting of aftermarket fibreglass seats the rules allow the back section of the rear sub-frame to be cut off as per the picture below.

If you retain the original rear plastic leave sub-frame as in place as the rear seat cowl needs it for support.

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Bodywork/Fairing.