The premier MX1 class was once filled worldwide 250cc two strokes. Start lines would fill with blue smoke from the pre-mix and mechanics would spend their time shuffling through jet boxes playing with an assortment of pilot, main and needles jets to tune their pride and joy. Long before the new generation four-strokes came along followed with EFI and a host of other technology that brings us to the current day.
Today 250cc two-strokes are a rare commodity, with many manufacturers choosing not to produce a quarter litre machine in anything other than a four-stroke. KTM have been one of the few manufacturers to stick with the 250cc two-stroke and have ramped up their efforts in the R & D department to ensure that they don’t become stagnant and fall too far behind the four-strokes. The all new 2023 KTM 250 SX brings quite possibly one of the most updated and technologically advanced 250cc two-strokes that we have ever seen!
CHANGES FOR 2023
KTM have completely reinvented their entire range of MX bikes for 2023. It is far and away easier to list the parts of the bike that remain unchanged. There is only a small list of parts that carry forward from the previous model, which includes:
- Brembo Brake system
- Wheels
- Voltage regulator
- Throttle Body
- Start Relays
- ECU
- ODI Grips
- KTM/NEKEN Handlebar
Other than these above, each and every remaining part has been changed or updated in some way. Here’s a quick overview of the major factors to consider with the new model.
- Direct Fuel Injection via a Keihin 39mm throttle body (Unlike the TPI Enduro model)
- Bike runs pre-mix fuel (Unlike the TPI Enduro model)
- Electronic exhaust valve
- Electric start only!
FIRST IMPRESSIONS
Upon first glance the 2023 KTM 250 SX looks sleek and aerodynamic with a distinctly pointed shape to the radiator shrouds and the striking orange seat complements the rest of the bikes livery. Upon arriving at the official launch I found myself jumping straight up onto it. Any ex-racer will relate that there’s something special about that first impression you get when you sit on a completely new model bike. Your brain is working overtime assessing the width of the tank, the flatness and profile of the seat, the relationship between handlebar, seat and footpegs and the shape and profile of the front mudguard.
The new KTM has a totally different feel to what I expected at first glance. The tank/seat junction is slightly wider with a much flatter profile to the top of the seat. I always found KTM’s in previous years to be a little too slim at the tank junction so this is a welcome change for me. The top of the seat cover has little ridges that provide an enormous amount of grip for a production bike and basically holds you in place.
I immediately noticed a much wider front guard that when combined with the seat/tank width gave a much chunkier first impression than before which is not necessarily a bad thing. The bike immediately felt comfortable and well balanced. I hopped straight up into the standing position with legs gripping through the back third of the motorcycle to assess the width.
For me this has been a bit of an issue with the KTM’s for as long as I can remember. They have a very slim seat/tank junction that blows out to an extremely wide gripping area near the rear where we spend most of our time. I was happy to find that the width barely changes from the front while seated, to gripping the rear while standing.
LET’S TALK FUEL INJECTION
KTM have opted to go for a completely different fuel injection system to that used in their enduro model two-strokes. Since 2018 KTM have used a TPI (Transfer Port Injection) system where fuel is injected straight into the barrel’s transfer ports via two injectors (this is not a direct injection system). This system doesn’t require pre-mix fuel.
For the 2023 SX two-stroke range the injection takes place via a Keihin 39mm throttle body utilizing two separate injectors. One fires constantly while the second fires through the mid to upper rev range. This new injection system requires pre-mix race fuel and utilizes an electronic exhaust valve to complement the whole process.
CHASSIS
The brand new frame design includes a new shock mounting position which KTM claims will give less interference with the steering head, improving handling. It also has more torsional and side stiffness, while the width is identical to its predecessor. One of the biggest key factors in the chassis department is the motor being rotated backwards two degrees via the engine mounts, resulting in a 3mm rotation over the previous model. KTM claim a benefit in ‘anti squat’ with their all new frame.
SUSPENSION
KTM have stuck with their WP XACT 48mm air fork with modified valving. The big change in the fork department is a new internal hydro stop which has been extended from 20mm to 40mm. The hydro stop provides a cushion effect when the forks bottom out on hard landings.
At the rear KTM has designed an all new shock with a new piston, fully adjustable hand adjusters and a new plastic spring holder. The new shock is 15mm shorter at 456mm but has a longer stroke at 140mm.
ELECTRIC START
All new for 2023, the complete SX range now comes standard with electric start via a toggle button on the right side of the handlebar with both the start and stop buttons in one.
BITS AND PIECES
- New footpegs have been introduced that are 8mm longer, 5mm wider and provide better contact to the bike.
- A new ‘hybrid subframe’ uses a mix of aluminium and composite materials providing more side impact stability. The top of the subframe is composite material while all the lower connection parts are aluminium.
- A newly designed swingarm is the same length as the current generation but with improved stiffness while shaving off 190gm. KTM have gone to a smaller 22mm rear axle to transfer that stiffness to the swingarm.
- The 2023 KTMs’ receive a new shock linkage and pull rod that has an identical linkage curve to its predecessor along with new triple clamps and an all new universal hour meter, the same part for all of the KTM models.
- The seat is held on by one bolt located at the very top of the seat near the petrol cap.
- New ‘unified’ radiators feature a special high pressure cap
- A new rear brake caliper with a 22mm piston
RIDE REVIEW
MOTOR
From the moment you hit the start button and click it into gear you’re reminded that you’re still riding a barking 250cc two-stroke. If any of you punters out there had dreams of this new fuel injection system turning it into an almost four-stroke style smooth power delivery you’ll be a little off the mark. The new 2023 KTM 250 SX still has all of its traits and characteristics that we’ve come to know over the years.
The moment you exit your first corner and roll the power on you’ll start to notice some major changes and your mind will be ticking overtime. The fuel injection completely transforms the way the power is delivered to the ground and you almost need to re-program your brain as to how a two-stroke should feel. When you first roll the power on the bike has quite a lean feeling as if it wants more fuel and it does take a little to get used to. Once you get into the midrange part of the power the second injector kicks in and that lean feeling is transformed into a fatter boost that inspires more confidence and a smooth rush of power.
Once you wrap your head around the way the fuel injection works and stop stressing about the lean bottom end you come to the realization that the bike actually has a very smooth transition from bottom end through to midrange. You just need to keep reminding yourself that the bike won’t bog from fuel starvation while tackling up-ramps!
The motor overall is extremely smooth and easy to ride, while also still having that punchy characteristic if you choose to ride it that way. I found the standard gearing to be perfectly set up for me and rarely found myself between gears. Top end over-rev did what it was supposed to and was predictable with enough power to get out of trouble. However I did find that the bike produced most of its usable power from bottom through to upper midrange with a very linear power curve.
There are two maps to choose from via a handlebar mounted switch. The white map is the standard one which delivers a mellow curve and the green map gives a more aggressive and lively delivery. I found that I preferred the green map as it seemed to bring the motor to life and enhanced bottom, mid and top-end power without sacrificing too much smoothness.
HANDLING
The track we were testing on at Conondale had plenty of ruts and a combination of dry ledges and muddy patches to keep you on your toes. I found the 250 to be reasonably settled in the tough conditions and the overall handling impressed me. I’m usually a harsh critic of air forks but I have to give props to the new bottoming system integrated into the WP XACT 48mm forks. They blew my mind as far as bottoming resistance went.
There is a huge jump on the track that measures over 140 feet with a really hard landing and the previous model WP forks would have really struggled with this. The new fork amazed me with its absorption capabilities on big hits. Small bump sensitivity was nice up front also but we didn’t have a huge amount of bumps on the track to truly put these forks to the test.
The shock held up nice under acceleration and didn’t do anything I wouldn’t expect it to do under brakes. Overall a nicely balanced suspension package, that when combined with the new chassis, provides a planted and confidence inspiring ride. Other than a little more pressure in the forks I didn’t need to play with suspension settings at all. We started off with 105mm ride height and that’s where I found myself happiest.
OVERALL
I must say that I am impressed with the latest edition 2023 KTM 250 SX. I really didn’t know what to expect. When a bike is released with the amount of changes that we’ve seen with this model it can really be quite hit and miss. The bike is so much fun to ride and without a doubt the new fuel injection really does smooth out that initial part of the power delivery.
Does it turn it into a four-stroke? No it doesn’t. Will it all of a sudden now be way more competitive against the 250cc four-stroke in a race situation? Not necessarily. For a huge proportion of the general public it will be a lot easier to ride, easier to tune and easier to start while opening up a whole new world of tuning. For those of you that are die hard two-stroke fans it still has enough excitement to blow your hair back.
TO IDLE OR NOT TO IDLE
If you’re an old school racer like myself, having done many years of lining up on two stroke machines then you’ll know what I’m talking about when I say that two strokes aren’t supposed to idle. If you went and asked Chad Reed or whoever your favourite two-stroke racer was if they ever had their two stroke idling they would say “hell no”.
These days, whenever I test a two-stroke whether it be for a manufacturer or an exotic old retro 500cc bike they always have their bike idling and I always ask “Do you mind if I wind the idle down so it doesn’t idle?” I hate nothing more than a two stroke that runs on into corners because the idle is set.
With the new fuel injection system on the 2023 KTM two-strokes the ignition and fuel mapping has all been programmed around an idling bike. As soon as the idle was turned down the mapping was out and it caused a flutter out on the track. Once we went back to having the bike idle my mapping issues were solved. So my advice to any two stroke enthusiasts out there that don’t like to have their bike idling, just give it a try and you will eventually get used to it, just like I did.
INJECTING ROOM
With the KTM EXC models already running TPI, we asked Customer Service Manager Rob Twyerould why the same fuel delivery system wasn’t used in the SX.
“TPI works well in the off-road scenario but for all out performance it has some limitations. Therefore the EFI two-stroke was developed for the competition models, retaining the pre-mixing of oil and fuel. The ability to tune not only the bikes fuel and ignition but now the electronic exhaust valve, allows greater control over tuning the power delivery”.
“With the SX versions not having to reach an emission standard (like the homologated TPI machines) EFI was the most effective way to match/improve the outright performance over the previous carburetted versions, and gain all the benefits that we know from the EFI four-stroke models”.
Specs
2023 KTM 250 SX
ENGINE
TYPE electric start, single cylinder two-stroke
DISPLACEMENT 249cc
BORE & STROKE 72mm x 66.4mm
COOLING liquid cooled
FUEL METERING Vitesco Technologies EMS
TANK CAPACITY 7.2 l
TRANSMISSION 5 speed
CLUTCH Wet, DDS multi-disc clutch, Brembo hydraulics
DIMENSIONS
SEAT HEIGHT 958 mm
GROUND CLEARANCE 354 mm
CLAIMED WEIGHT 99.4 kg dry
SUSPENSION
FRONT WP XACT-USD, Ø 48 mm, 310mm travel
REAR WP XACT Monoshock with linkage, 300mm travel
BRAKES
FRONT 260mm disc
REAR 220mm disc
CONTACTS
BROWSER
BLOWER
1800 644 771
WARRANTY
1 month
This 2023 KTM 250 SX article appeared in ADB magazine issue #517
Words | Lee Hogan
Photos | KTM Australia
