For years it’s seemed certain that two-strokes were going the way of the dodo – edged out by emissions requirements and their cleaner four-stroke cousins. Now a new range of two-stroke KTM enduros shows that the design’s death might not be as close as it had appeared.
The new two-stroke KTM engine – made in 250cc and 300cc forms – uses transfer port injection (TPI). That’s a little different to previous attempts at injecting two-strokes using throttle body injection or direct fuel injection. Throttle body injection has many of the same flaws as carburetted two-strokes, so has been largely ignored. Direct injection, as tried on the Bimota V-Due and various others, is hard to make work as there’s little time between injection and combustion for the fuel to atomise properly.
KTM’s patented system uses two injectors to add fuel in the transfer port. It doesn’t need to be mixed with oil, as it’s no longer lubricating the engine’s bottom end. Instead there’s a four-stroke-style lubrication system. It can also be injected later, so less fuel can reach the exhaust port before it closes.
The first bikes to get the system are the 250 EXC TPI and the 300 EXC TPI. They gain the injection, a new ECU, a new throttle body and an array of sensors to make the system work. The cylinder head is also new, as is the oil pump and air box. The oil tank is in the frame.
KTM spokesman Joachim Sauer said: “It is a very proud moment for us to unveil the world’s first serial electronic fuel injection two-stroke offroad competition bikes. We at KTM are committed to developing revolutionary technology, and with the KTM 250 EXC TPI and KTM 300 EXC TPI models we feel the game has once again been changed, as this is a global first. Our goal was to create a 2-stroke Enduro bike that would not be incredibly complex, while also retaining the feel of a carbureted machine, yet with all the benefits of fuel injection. This includes the elimination of the need to pre-mix fuel or change the jetting for different environments, which is a major benefit to the rider for hassle free, two-stroke fun.
“In addition, the EXC TPI models provide improved comfort with a prompt but consistent power delivery, while also offering a vast reduction in fuel consumption. Not only does the EXC range provide top performance and outstanding rideability with the lowest weight in each class, the intuitive handling of these bikes with their high quality serial components is something we’re synonymous for and we’re really looking forward to these new machines reaching dealer floor.”
The bikes are due on sale at the start of June.