honda cbr125

does anyone know how i can tweak a cbr125 so that i can get 10,20 or even 30mph onto the top speed?

If its parts like lighter pistons etc,could anyone tell me any websites were i can get performance parts for the cbr125?


Your going to need about £600 for a start but here we go…

You need a 170cc kit… I suggest the product linked as it adds 45cc with little hassle. What good does the 45cc do? Well if you buy the biggest fuel jet you can which is about £4 and is easy to put in then you will gain about 5 horse power. Or take the top speed to a nice easy 90mph. You have to however put bigger sprockets on. Increase the front sprocket by 2 teeh and decrease the rear by 2 teeth if you can. This makes the power more usable across a taller gear effectively.

You could also do with a full Devil race exhaust or ANY full stainless steel exhaust and get the baffle out of it as its still within the legal limit with it out.

This will clear its throat and make it produce maybe an extra 2 horse power.

Then it gets easy, an iridium spark plug, a K&N racing air filter, and open the airbox as much as possible unless the air filter is designed to replace the box.

That will take its top speed to somewhere in the region of 100-110mph as the torque you will be making will be sufficient for it. I have held 85mph on a CBR125. It read 93 on the clocks. It is possible just it costs A LOT to get it to that point.

nice 1 matey pips…thats deffos food for thought lol…ill have to start saving up haha

if i was to start with one thing,would it be easier to get the exhaust as it just replaces the stock exhaust without having to cange anything?


You can keep it the same. You dont need to change anything really. I think if anything the exhaust will make the bike run a little bit lean. Which isnt particularly the best thing for the bike but it will give it a small amount of extra kick.
The main jet for the carb should only be about £5. You just drop off the bottom of your carb and take out the main jet and replace it with the other. Then its running rich which is exactly what you want I would say :slight_smile:

You can squeeze out a few extra mph without increasing CC but you will accelerate to your top speed with a lot more ease.

Not being funny but you’re better off spending the money on passing the DAS and getting a big bike. Not only will you be spending your money on the parts but your insurance will increase dramatically. Also when you come to sell your bike it won’t be worth anything that you’ve spent on it.

yeh very good point mate…cheers,i think ill do that :wink:

erm WTF ???

next you will be saying to change from a blue power band to a green one …

I had an indicated 92mph out of a CBR125 with that modification :laugh:

I was tucked right in of course and weigh a mere 11 stone but it got there. True speed probs was about 80mph though. This was on the A1 heading to Peterborough on the monster long flat before the junction to get to the BMF show.

The best any of my friends has ever got out of a CBR125 was a upgraded one like I mentioned that did an indicated 107mph. It required the wider rear tyre as going to that speed began causing severe stabilisation problems.

but you dont just buy the biggest jet in the world for the bike, the jet(s) need to be the right size for petrol/air mixture.

im just gunna leave it be and concentrate on/save the money for passing my bike test:cool:

Correct, with the K&N air filter which is a cone providing extra air flow combined with having the carb reset to handle it. I have to do it sat down with the manual for the carb to manage it myself.

Though I would like to add just putting on a bigger jet is far better than increasing air flow. Running it lean is a bad idea compared to it running very rich with the bigger jet. When you set up the carb for better air/petrol distribution you are meant to always set it to run rich.

were can i get a 170 kit for the cbr i have a 2005 cbr dose any one have one i can buy or any tips on what to do