[New Arrivals]

Tested: KTM’s 2018 Two-Strokes

2 years ago | Words: Andy Wigan | Photos: Andy Wigan, KTM Images, Sebas Romero

Recent PR from KTM made it clear that their 2018 two-stroke enduro models would use an all-new fuel-injection system called TPI (Transfer Port Injection), but there wasn’t a lot of detail provided about how it would work, its costs and benefits, or what impact it would have on the 2018 bikes’ performance and character. Having ridden the 2018 bikes for a day at the international media launch at Erzberg, Austria, we can now answer those questions.
Obviously, we’ll go into much more detail in the coming weeks, but to help put these new bikes in context, Transmoto‘s Andy Wigan filed this rapid-fire, Q&A-style report from Austria for a timely, top-line insight into the new 2018 KTMs.


At this stage, only the 250 and 300EXC enduro models (and the up-specced Six Day machines based off them) get the new TPI fuel-injection system.


Fuel is now injected into the barrel’s transfer ports via two injectors. By injecting the fuel against the airflow direction in those ports (rather than injecting directly into the combustion chamber), KTM found it created a much better mixing of fuel and air, and a more efficient combustion. The oil still finds its way into the engine’s crankcases, but that’s now via a 39mm throttle body, not a carb. The oil is fed at low pressure from a 700ml tank that’s mounted under the seat, and atomised by the reed block. By separating the way fuel and oil are ingested by the engine, there no longer needs to be a compromise in the fuel-to-oil ratio to ensure engine parts are adequately lubricated. Instead of the 50 or 60:1 ratio recommended for KTM’s carb-fed two-strokes, the 2018 bikes run at anywhere between 70 and 100:1, depending on a number of engine parameters (RPM, throttle position, load, etc). No special oil is required for the TPI machines. KTM recommends you use the same Motorex oil (Cross Power 2T) as you did to premix your fuel with the carburetted two-strokes.


At the launch, KTM confirmed that they had developed two main direct-injection systems for their two-strokes, but none of them managed to match the carburetted bikes’ performance – in terms of outright power, feel and sound (yep, KTM was adamant that that certain something that makes a two-stroke a two-stroke – much of which has got to do with their trademark exhaust note – was not compromised). As outlined by KTM’s Product Marketing Manager, Joachim Sauer, “We wanted to keep the rideability and engine characteristics as close as possible to our well-established carburetted engine, while eliminating the disadvantages of the carburetted engines – the need for re-jetting for different elevations, humidity, etc, for instance.”


The impetus for the move to an EFI system for KTM’s two-strokes was the Euro 4 emission regulations, which come into effect for 2017. But because Euro 4 applies only to road-going or registered vehicles, KTM has only fitted the TPI fuel injection system to its enduro bikes. Their SX models will remain carb-fed (for the time being, anyway).


The obvious benefits of the TPI system are: lower emissions (by up to 50%), less smoke, lower fuel consumption (20-40%), and the system’s automatic adjustment for altitude changes means no need to ever re-jet the machines. On top of that, you have some practical advantages – such as no fuel spillage or flooding when the bike is upside-down on a mountainside (or in the back of your van), no need to carry premix oil in your backpack (the 700ml oil tank lasts for four to six tanks of fuel). From a performance point of view, it facilitates easier starting and idling, and a smoother and more rideable power delivery.


Getting rid of the carb saves some weight, but by the time the TPI bikes are fitted with the new oil tank, fuel pump and associated sensors and electrical system mods, there’s a net increase in weight of 2.5-3kg. Also, KTM’s enormous investment into this technology will ultimately be paid for by the consumer. KTM Australia’s Jeff Leisk says he expects the 2018-model 250 and 300EXC TPI bikes (which arrive in Australia early in 2018) will retail for approximately $1000 more than their carb-fed equivalents (which will start arriving in Australia in August). Limited numbers of the 2018 250/300EXC Six Day models (which only come in the TPI configuration) will be available in October.


There is an alternative (softer, traction) map already programmed into the bike, which can be activated by disconnecting the map cable behind the headlight (a map select switch only comes as standard on the Six Days models, or can be purchased from KTM’s PowerParts range for standard models). As with KTM’s four-strokes, it is not possible to create custom maps for the 2018 two-strokes. And despite many people thinking that the more sophisticated EMS required for these injected two-strokes would also pave the way for traction control, KTM’s design team says traction control for their two-stroke models is at least three years off.



Not much has changed on the cylinder design. Now, to remove the barrel, the only additional step required is the disconnecting of two electrical connectors and the fuel line that runs to the injectors. This is a simple dry-break connector, as used on the fuel-injected four-strokes. The addition of the oil tank makes it a little more cluttered around the top shock mount, but as far as we can tell, access to key components for maintenance or adjustment has not been affected. KTM tells us that recommended service intervals for the TPI and carburetted models are the same or very similar.


KTM acknowledges that the system is more complex and involves more parts (there’s a fuel pump, oil pump, injectors and sensors that are not required on carburetted models). But they also make the point they’ve tested the system extensively and found no issues, and that many of the new hardware parts are the same or similar to those that have proven their reliability in their four-stroke models.


Yep, but only a few. Aside from the new graphics, the hand guards are now white, the fork protectors are now black and the radiator louvres are redesigned to prevent them from clogging up with mud as easily. Plus the front of the two-strokes’ fuel tanks have been modified slightly to create more room for the oil filler cap (which now sits on the frame’s backbone, just behind the steering head). But the biggest change is to the settings in the WP Xplor fork that was introduced across KTM’s entire enduro range last year. By better marrying the flex characteristics of the Xplor fork’s inner and outer tubes, KTM found that they could get a more compliant action from the fork over small bumps, and this has allowed them to firm up the fork’s compression damping. Spring rates remain unchanged on all models, but the bolstered damping across the range helps hold the fork up in its stroke better, improves progression and assists bottoming resistance.


In a word, brilliantly! Compared with the carb-fed 250 and 300EXC, the 2018 TPI models start easier, idle more smoothly, and rarely emit any blue smoke or pungent two-stroke smell. Their overall power character doesn’t feel much different from the predecessors’. The TPI bikes’ engines are definitely a little smoother and more responsive to throttle inputs, which gives them a really torquey, tractable feel. And the things remain perfectly jetted as we moved from an elevation of 800 to 1500m at Erzberg. That in itself was astounding. For me, the 300EXC TPI was the standout machine. While the carb-fed 250EXC has closed the gap on its 300cc sibling in recent years, the TPI-fed 300EXC extends it again. It’s noticeably more torquey and responsive, and eats hills for breakfast. And, contrary to what you’d think, it also seems to pull harder for longer than the 250 at high revs. In other words, the 300EXC TPI feels like it’s been a greater relative beneficiary of the new technology.
Meanwhile, the upgrades to the Xplor fork work a treat. The introduction of the all-new rolling chassis for 2017 (with Xplor fork and shock) firmly established the KTMs (and their Husqvarna counterparts) as the benchmarks when it comes to enduro bike handling. And the mods to the 2018 bikes’ fork gives the new bikes an even more poised, predicable and confidence-inspiring ride across all sorts of terrain and obstacles.


Epic! Don’t even start me, cos I’d prattle on about it for hours.

Want to see the bike in action?

Watch Transmoto‘s Andy Wigan’s ride impression after to throwing a leg over the new machines. 

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