Rajan Wilcox
KTM's new line of Transfer Port Injection TPI two-stroke motorcycles has sparked interest and discussion among riders and motorcycle enthusiasts. The TPI system, which injects fuel into the barrel's transfer ports, aims to improve fuel efficiency and performance. KTM's 2018 introduction of fuel injection to its two-stroke models marked a significant evolution, addressing the challenges of carbureted engines while retaining the benefits of two-stroke engines, such as raw power and lightweight design. The TPI technology also promises a more eco-friendly era for two-stroke motorcycles, reducing high emissions and improving fuel efficiency. While some riders have expressed concerns about glitches and reliability, others have praised the advancements, such as counter shafts and vibration-free rides. The fuel-injected KTM two-strokes have sparked a love/hate relationship, with some riders eagerly awaiting further iterations and improvements.
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What You'll Learn
KTM's switch to oil injection
The switch to oil injection also removes the need for human mixing ratios, which vary from person to person and are not ideal for consistent performance. Instead, the ECU can handle the amount of fuel and the timing of delivery based on information from the sensors. This means the system can account for differences in gasoline across the world while remaining simple and reliable. The computer part of the KTM is built by Synerjet, a company owned by Continental with extensive experience in engine management electronics.
The TPI system was discovered by KTM almost by accident in 2014, with the first prototype appearing in 2006. The system was developed in collaboration with Australian company Orbital, and KTM has since patented the technology. The TPI system has been called one of the most important projects for KTM's design team, and the most significant change ever made to KTM's two-stroke models.
While the TPI system is more complex, with more parts that can break, it has been tested and proven reliable. The technology is also similar to that found in KTM's injected four-stroke engines. The carbureted bike will still be available for at least another year in the US, with KTM offering one FI-equipped model for 2018, the 250 XC-W TPI.
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KTM's TPI technology
KTM's Transfer Port Injection (TPI) technology is a fuel injection system that was introduced in 2018 for the company's two-stroke off-road motorcycle models, namely the 250 EXC TPI and 300 EXC TPI in Europe, and the 250 XC-W TPI in the US. This technology is notable for being the world's first serial production fuel-injected two-stroke motorcycles.
With the TPI system, fuel is injected into the barrel's transfer ports via two injectors, rather than directly into the inlet port, head, or combustion chamber. This method of injecting fuel against the airflow direction in the transfer ports creates a better mixture of fuel and air, resulting in more efficient combustion. The oil is fed at low pressure from a 700ml tank mounted under the seat and atomised by the reed block. By separating the way fuel and oil are ingested by the engine, there is no longer a need to compromise the fuel-to-oil ratio to ensure adequate lubrication of engine parts. As a result, the 2018 bikes can operate with a much higher fuel-to-oil ratio, ranging from 70 to 150:1, depending on various engine parameters such as RPM, throttle position, and load.
The TPI system also features a separate lubrication system, with an oil pump controlled by the Electronic Control Unit (ECU). The ECU manages the amount of oil that enters the engine based on load and RPM conditions. This eliminates the need for pre-mixed fuel, helping to reduce emissions. Additionally, the TPI system reduces fuel consumption during low speeds by up to 40%, although consumption remains unchanged at wide-open throttle.
The development of the TPI technology faced challenges, such as initial flameouts due to the need for a more sophisticated Engine Management System (EMS) to manage fuel metering. However, KTM was able to overcome these issues, and the TPI system proved successful, with positive riding impressions and improved performance. The TPI technology also simplifies maintenance, as it shares similarities with KTM's injected four-stroke engines, which have proven reliable.
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KTM's two-stroke engine evolution
In the 1980s, KTM continued to innovate with its two-stroke engines, introducing its first water-cooled two-stroke, the 125cc LC, in 1981. In 1982, KTM entered the MXGP with a rotary-valve engine, and in 1984, they introduced the 125cc GS, featuring KTM's first full reed-valve intake into the crankcase. In 1985, KTM's 250cc engine was fitted with a digital ignition, and in 1987, their 125cc and 250cc engines were fitted with power-valves. The 1990s saw the release of a 250cc engine with twin-valve control in 1990 and a 125cc engine with twin-valve control in 1997.
The early 2000s marked a significant shift for KTM's two-stroke engines, with the introduction of electric-start technology in 2008 for the 250cc and 300cc models, heralding a revival of the two-stroke dirt bike market. In 2014, KTM's breakthrough 'Transfer Port Injection' (TPI) system was discovered, marking a pivotal moment in the company's fuel injection R&D program. This system, developed in collaboration with the Australian company Orbital, aimed to address the challenges of fuel injection in two-stroke engines.
In 2017, KTM introduced a new-generation 250cc engine with a counter-balancer, reducing vibration and enhancing refinement. The following year, KTM unveiled the world's first fuel-injected production off-road competition motorcycle, equipped with the revolutionary TPI technology. This innovation allowed KTM to meet stringent Euro4 regulations for noise and emissions without compromising performance. The TPI system improved fuel-to-oil ratios, resulting in more efficient combustion and better fuel mileage.
In 2020, KTM continued to refine the TPI technology, improving performance and rideability. The 2023 MX models, including the 125SX, 250SX, and 300SX, transitioned from carburetors to TBI fuel injection technology, and in 2024, KTM's two-stroke enduro models adopted the same TBI system, meeting the latest Euro5 emission regulations.
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$64.34
Fuel injection vs carburetor
KTM's Transfer Port Injection (TPI) technology has been a significant change for its two-stroke models. The TPI system injects fuel into the barrel's transfer ports via two injectors, creating a better fuel-air mixture and more efficient combustion. This system also separates the way fuel and oil are ingested, eliminating the need for a compromise in the fuel-to-oil ratio.
Fuel injection systems, in general, offer precise fuel control and reduce fuel wastage. They consist of electronics and sensors that control the fuel supply and deliver the best air-fuel mixture possible based on parameters like engine speed, load, and throttle position. However, they are more complex and costly, and some argue that carbureted engines are easier to repair and maintain.
Carbureted engines have been traditionally used in motorcycles and are well-loved by the community. Carburetors have a float-type chamber where fuel is collected and distributed to the induction system. By using the venturi effect, the fuel is vaporized and mixed with air before entering the engine. The throttle controls the airflow, while the mixture controls the fuel-air ratio. Carbureted engines are also easier to start in cold weather and can be kick-started, unlike fuel-injected engines that may require a battery.
When it comes to performance, a well-tuned carburetor can theoretically match or even outperform a fuel injection system at wide-open throttle or high RPMs. However, fuel injection systems excel in other aspects, such as consistent performance, efficient fuel usage, and immunity to issues like float bowl slosh.
While the motorcycle community has been hesitant to fully embrace fuel injection technology, KTM's TPI system has shown promising results in terms of efficiency and performance. The TPI bike has better fuel mileage, and its fuel injection system prevents issues like fuel dripping from vent lines and excess unburnt fuel, commonly seen in carbureted engines.
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KTM's two-stroke fuel injection feedback
KTM's two-stroke fuel injection technology has received mixed feedback from the motorcycle community, with some riders embracing the change while others remain sceptical or loyal to carbureted bikes. Here is a detailed look at the feedback:
Performance and Efficiency:
Many riders have noticed an improvement in performance and efficiency with KTM's fuel-injected two-stroke models. The Transfer Port Injection (TPI) system, introduced in 2018, creates a better mix of fuel and air, resulting in more efficient combustion. This leads to better gas mileage, with some reporting that the TPI bike burned less fuel than its carbureted counterpart on the same 30-mile loop. The TPI system also eliminates the need for a compromise in the fuel-to-oil ratio, allowing for a wider range of ratios depending on engine parameters.
Smoothness and Refinement:
Some riders have praised the smoothness and refinement of KTM's fuel-injected two-strokes. They have noted that the bikes are "vibration-free" compared to carbureted models, offering a more refined and smoother riding experience. The electric start feature, combined with the kickstarter backup, provides added convenience and reliability.
Reliability Concerns:
However, there have been concerns about the reliability of fuel injection in KTM's two-stroke models. Some riders have experienced issues with the 2023 models, but it seems that these gremlins have been ironed out over time. There are also worries about potential electrical problems, with one rider mentioning that their 2023 KTM 125 XC ran well, but they still preferred the carbureted option.
Adapting to New Technology:
The motorcycle community, known for its reluctance to embrace new technology, has had a mixed response to KTM's fuel injection. While some riders are open to the change, others are hesitant and prefer the familiarity of carbureted bikes. KTM acknowledged this by offering carbureted models alongside the FI-equipped ones for a period, understanding the need for adaptation.
Overall, while there is some resistance and teething problems, most riders seem to agree that fuel injection is the future, and many are expected to adapt and appreciate the benefits of KTM's fuel-injected two-stroke models. The TPI technology, in particular, holds promise for improved performance, efficiency, and ride quality.
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Frequently asked questions
The KTM 250XC-W TPI has a fuel capacity of 2.6 gallons.
KTM's 2-stroke bikes use the Transfer Port Injection (TPI) system, which injects fuel into the barrel's transfer ports via two injectors.
The TPI system offers better fuel-air mixing, improved combustion, and higher fuel efficiency compared to carburetors. It also eliminates the need for a compromise in the fuel-to-oil ratio, resulting in a cleaner and more efficient engine.
KTM's fuel-injected 2-stroke bikes aim to deliver the benefits of a traditional 2-stroke engine, such as raw power and lightweight, while reducing emissions and improving fuel efficiency.
