Real dirt: Living with a KTM 125 SX

Real dirt: Living with a KTM 125 SX

The fun machine!

Our little KTM smoker is a hoot but needs some fine tuning

By Dave Willet. Photos Adam Duckworth

It’s been a long time since I enjoyed riding a bike as much as this. It’s an absolute weapon! The weather in the past few months hasn't been too bad so the 125 has seen lots of action. I've ridden a few tracks and even treated the little ripper to some laps around Jake Nicholls’ personal track which is incredible. It's a GP-style circuit so not for the faint hearted, that's for sure. But after a few laps I grew some balls and nailed the jumps!  To be honest, the bike makes good BHP so enough power to do the jumps is never in question- as long as you’re brave enough and have the skill.

Jake Nicholls puts our bike through its paces

Even the suspension in standard form is good enough, too. Jake put in some fast laps on the bike and said it was OK too, which is quite amazing considering we’re both not super-lightweights and Jake really hits things very hard and fast. It's not all roses, though. Anyone experiencing difficulties setting up the carburettor on their beloved two-stroke 125 KTM, don't worry as you’re not alone. The issue isn't so bad if you’re hard on the throttle but if you are a rider that feeds the power in, you maybe be struggling.

Pumping up the suspension should be done every ride

All the KTM and Husky 2017 two-stroke range share the same new carburettor yet the Husky seems to be a little more suited to the change. Perhaps that’s due to the bike’s different airbox and the different air flow it offers.

But the fact still remains the bike is set too rich from stock - meaning fuel overload! If your two-stroke is bogging when landing off jumps, or there’s a delay in power when exiting the turns, you may need to do some carb tweaking. We’re investigating and will bring you updates soon.

The 250 suffers, too, but it’s the 125 that has the worst symptoms. The performance is fine once you’re running past quarter throttle and the main jet takes over.

Yep, she flies just fine!

I've also had issues when rolling off the throttle into a turn. The motor just seems to load up with too much fuel which gives a delay when cracking the throttle back on and exiting the turn. This doesn't happen on every turn but it's enough to make me adjust the carburettor as it's clearly not on point.

The speculation is that KTM were very close to bringing out a fuel-injection two-stroke for 2017 but production issues meant they pulled the plug at the last minute. Rumours are it's coming for 2018 and they’ve already been testing an EFI bike in enduro competition.

Is the carb here to stay?

Now we believe these rumours of an injected two-stroke motocrosser to be true as the signs are clear to see. KTM changed carburettor manufacturers for 2017 from Keihin to Mikuni because Keihin wanted a three-year commitment to supplying carbs. Mikuni would supply smaller batches, so they went that way. Chances are it’ll be a Keihin injection system on the way in 2018 though.

On our KTM I've replaced the stock exhaust system with a full aftermarket DEP. I’ve got a shorty tail pipe as they look trick but it also sharpens up the hit of power too. More power needs more fuel so a performance pipe actually cleans up the power delivery of the stock carb.

The next thing I did was drop the pilot jet to a 42.5 instead of the stock 45. You can drop down one clip position in the needle too but I'd be careful when doing this, especially this time of the year. If you’re a typical club rider it should be fine but any faster and it’s important you do a plug check.

I'm currently running mine in stock position but this was before the tracks started to sap power from the motor. So since the drop in temperature, I've played it safe. Better safe than sorry!