Introducing our Kawasaki KLX250S Project Bike

It’s time we got a bit dirty and get off the beaten path. In addition to our little Ninja 300 track bike we’re building, we’ve decided to also take the bullet proof (but overall fairly uninspiring) KLX250S dual sport and upgrade it to a true all rounder with a heap more poke and versatility.


The reason we chose the KLX250S boils down to a few factors. One is that they’re extremely cheap second hand, with ours costing a little under $3,000 despite being only three years old. Secondly, the KLX250S has been around for a very, very long time and is renowned for being near indestructible. Thirdly, while it’s a solid machine there’s a huge amount of work we can do to it which really is the point of a project bike at the end of the day.

Our first job upon getting the bike was a full service – engine oil, brake oil, new filters (both engine and air), replacing the brake fluid and a new spark plug. While the bike was in good condition, it hadn’t had a service done on it for over two years. That could best be seen around the chain – it was completely coated in a combination of old lubricant, dirt and anything else it attracted, making a lovely sludge that was difficult to get off even with kerosene. It necessitated taking the chain off in the end and soaking it in a solution for a few hours and then scrubbing it.

Even the grunge brush struggled with the build-up of scum.

Even the grunge brush struggled with the build-up of scum.

In addition to doing a full service, we also swapped out the standard front sprocket and replaced it with a slightly larger 13 tooth one. Given how the KLX250S is geared in stock form, it actually provides a pretty decent improvement in rideability – the front wheel is now far easier to lift, while top end speed remains unchanged.

Next stop was replacing the tyres and we chose a pair of Pirelli MT-21 boots – they’re close to full knobs while remaining road legal and given how soft the rubber of the tyre is, provide good grip on the road. They won’t last long though and we’re not expecting to get more than 6,000 kilometres out of them – plus or minus depending on how much time we spend on the bitumen with the bike – but that’s the trade off with such a tyre and we’re very happy with it so far.

New Pirelli MT-21 tyres provide good off and on road grip.

New Pirelli MT-21 tyres provide good off and on road grip.

The only other mod we’ve made to the bike is installing a small USB charging outlet which we connected via the ignition, meaning it will only draw power while the bike is turned on. We’ll see how it lasts given it cost $10 on eBay, but at the moment it’s only needed to maintain phone charge while we’re using it as a GPS.

So what next? Well, a lot. Our first major upgrade will be to the top end of the engine by getting a big bore kit. Normally we’d spend our money on improving the bike’s handling first, but we’ll make an exception with the KLX because in stock form it’s gutless and at 134kg it’s not exactly the lightest off road machine either.

The cheapest route for a big bore kit is to buy a locally sourced OEM 300cc kit from Kawasaki, but despite the reduced cost we’re thinking it’s still probably not worth it given only a 50cc bump in capacity. Instead, we’ll be looking at a 351cc kit from a company called Bill Blue who have been selling kits for the KLX250 for many years. That should improve horsepower and torque by a whopping 30 to 40 per cent – which isn’t hard coming off a low base but will absolutely transform the bike. That will potentially also allow us to change the bikes gearing even further to allow it to coast along in first gear when off road with less clutch input.


After that we’ll be installing a larger capacity fuel tank as the stock one only gives us around 150 to 170 kilometres range – an upgrade will hopefully see that rise to around 250 klicks. And while the bike came with an aftermarket pipe, it’s still using stock headers and is obnoxiously loud. We’ll be replacing both the headers and the pipe for something that provides a bit more horsepower and hopefully a little less noise.

Other additions and modifications to the bike that we’ll fit in where we can include:

  • Replacing the chain and ensuring it uses a rivet link instead of a clip-on link
  • Valve emulators for the front forks
  • New bars, as the stock one are known to bend very easily
  • Skid plate
  • Fender eliminator because the stock fender looks like poo.
  • Folding mirrors
  • Luggage rack
  • Lithium ion battery to save a few kilograms of weight
  • Aluminium rear sprocket for weight saving too

We’ll hopefully have our first update early next year with the big bore kit installed.


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