Carburetors vs. Fuel-Injection

CARBURETORS USE THE VACUUM CREATED by the intake stroke of the engine to force air through their ports and passages. As the air flows through, it simultaneously forces fuel into the combustion chamber.

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Fuel is then fed through tiny passages called "jets," which control how much gas flows into the combustion chamber-most carbs feature two jets, with the main jet controlling the fuel mixture at mid to high RPMs and the pilot jet controlling from idle to the middle of the rev range. While carburetors are elementary in function, tuning them properly is a long and arduous job that only veteran mechanics have perfected.

"Once you have a two-stroke 95 percent of the way there, that last 5 percent is really what's difficult to get down," says Joe Adragna, an amateur motocross racer who rode two-strokes throughout his childhood.

While a carburetor allows you to adjust the air-fuel ratio, it's more of a set-it-and-forget-it type of device. Fuel injection (or throttle-body injection in the case of KTM's two-strokes) is continuously variable. The process is now controlled automatically via an onboard engine management system that ensures a near-perfect air-fuel ratio all of the time. With more usable power and higher fuel efficiency, these engines feel much closer to a four-stroke when twisting the throttle open.

"We saw the benefits on the four-stroke side when we made the switch from carb to EFI more than 14 years ago," says Bretterebner. "Some of these benefits apply even more on a two-stroke engine, which is more sensitive in terms of air-fuel ratio."