2017 KTM 250EXC & 300EXC: Jetting Specs

As conveyed in the first video instalment about our 2017 250EXC project bike, KTM’s new-generation two-strokes have made huge performance gains for 2017. But if there’s been one gripe about KTM’s all-new, 2017-model 250 and 300EXC models, it’s been about the too-rich jetting specs the bikes arrive with. The new Mikuni carb doesn’t create any horrible flat spots or bogging under load, but it does come with pretty rich settings, meaning there’s definitely room for improvement in the bike’s jetting. And that’s not surprising, given that this is the first run of Mikuni carbs in a brand new engine with a brand new intake and exhaust.

In the course of putting 12 hours’ run-time on our 250EXC project bike, we’ve been refining its jetting specs along the way – with help from the guys at Australia’s biggest KTM dealer, KTM Newcastle, and technical staff from KTM Australia. And the good news is that small jetting tweaks not only make the bike’s engine run a whole lot cleaner and crisper, but it also increases fuel range by 40% (from 80km to 110km) on the 2017 two-strokes’ 9.5L tank.

The table below summarises the standard jetting that comes in the bike, the settings developed by KTM Newcastle, and the settings we’re currently using in our project bike. The leaner settings make the engine run much more efficiently, producing smoother and more progressive power, and better throttle response.

*Note: Theses jetting specs are based on a premix ratio of 50:1, using Motorex CrossPower (fully synthetic) 2T oil in 98 Octane fuel (from a Caltex, BP or Shell servo).

We’ll be working together with KTM Australia in the coming months to see whether we can improve the Mikuni carb’s setting ever further, so keep an eye on Transmoto’s website for developments and updated jetting tables that’ll help you set your bike up to suit various temperatures and altitudes.

Interestingly, KTM Newcastle is now providing a free jetting service for anyone with a 2017 KTM machine – even if you didn’t purchase a bike through them. So if you aren’t confident with carby tuning, give the crew at KTM Newcastle a buzz to organise a date and time to drop off your bike (remembering to bring your the jetting kit supplied with the bike). Visit their website here for contact details.

Here’s a comprehensive insight into KTM’s entire enduro bike line-up for 2017 (two- and four-strokes), and a video from the landmark new model’s international media launch in Spain.