KTM 690 Duke will give you quite a start

In a market dominated by torque-y V-twins and high-speed in-line fours, the single cylinder is the DustBuster of street bikes.

But KTM’s new 690 Duke could change the single’s long-standing reputation as an underpowered slow-poke. New for 2008, the Duke is the highest-performance production single to hit the market, cranking 65 horsepower from its 327 pounds.

That power-to-weight ratio may not sound like much to middleweight sport-bike riders, but they’d do well to remember the Duke’s name. That way they’ll know what’s catching them in canyon corners.

Best known for its race-oriented dirt bikes, the Austrian manufacturer has spent the last year leveraging its high-performance status with offerings in other power-sport segments, such as sport quads, a track car and street bikes. The 654-cc Duke is KTM’s third pure street model -- a naked bike follow-up to the 1,000-cc V-twin Super Duke it introduced last year.

The Super Duke was born from KTM’s Adventure dual sport, but the Duke’s lineage is more off-road. It uses a similar chassis and is powered by the same LC4 motor as KTM’s 690 Enduro and 690 Supermoto bikes.

The LC4 was introduced in 1988 and got various updates over the years, but it was seriously overhauled for 2007 -- an update that transformed the quivering, 640-cc, 44-horsepower motor into what KTM is now calling a modern single-cylinder four-stroke. In its new incarnation, the liquid-cooled LC4 is fuel injected (for better performance), counterbalanced (for less vibration) and more powerful (for reasons I don’t need to explain).

While the air box on the motor was enlarged, most of the power enhancements were achieved through a redesign of the cylinder head. Taking a cue from the automotive world, the new LC4 uses hollow shafts on its four intake valves, which make them lighter and faster, so the engine can rev higher and more quickly to produce more power.

When you’re riding the Duke, it’s clear the LC4 was developed for racing because it’s happiest when the grip is twisted. In lower gears at low and middle revs, the throttle was a little glitchy when I held it steady.

The Duke wants you to ride it as if money’s at stake. It wants you to accelerate, then brake hard, so you can take advantage of the slipper clutch and the race-inspired four-piston/four-pad radially mounted caliper and 320-mm front disc brake -- all of which work exceptionally well.

The bike’s maximum speed tops 100 mph. By how much, I don’t know. I wasn’t inspired to take it to three figures because the bike’s “ultra compact front mask with wind deflector” lives up to only the first four words of its name.

The seat was also a little problematic, and not because of its height. Admittedly, at 34 inches, the saddle is tall, but it’s also narrow, so I was able to reach the ground. My issue with this dirt-style banana seat was the finish. It was so slippery, it almost felt waxed. That was moderately aggravating when I was riding the bike the way it wants to be ridden -- accelerating hard and braking quickly -- both of which sent me sliding.

In terms of aesthetics, the Duke shares the same angular good looks of its big brother, the Super Duke. The artfully chiseled bodywork is fitted to an equally artistic chromoly trellis frame, which is underslung with a catalyzed exhaust.

The royal details are fitting on the Duke, even if the bike as a whole is just shy of true nobility.

susan.carpenter@latimes.com