Whether racing for glory or honing riding techniques at track days, getting on the gas earlier, accelerating quicker and attaining full throttle with the least possible effort is paramount to cutting faster lap times. Unfortunately, this doesn't necessarily jive with the design brief for production sportbikes, which spend 99 percent of their lives on the street. Quickly twisting the go-stick with abandon on the sometimes-sketchy traction of public pavement can be a recipe for disaster.
For this reason - and likely to satisfy manufacturers' legal departments - the bikes we buy come with relatively lazy 1/4-turn throttles that don't require super-precise modulation. For a cheap-and-dirty fix, some riders modify their stock throttle assemblies for quick-turn ability or swap their bike's throttle tube for a quicker one (Yamaha R6 and R1 throttles seem to be popular; the 2004 R1's is reputed to be a 1/6-turn unit).
Another route is to buy a quick-turn throttle, such as this Euroracing piece, which can be seen on race grids around the world and is distributed in the U.S. by Yoyodyne, a dedicated east coast racer-supply house.
Sold "for racing use only," Euroracing's throttle has a CNC-machined aluminum body, an aluminum throttle tube and is available in black or silver, with model-specific replacement throttle cables for more than 60 bikes. Unlike stock, fixed-action throttle assemblies, this adjustable unit comes with a trio of different-sized internal rotors - the largest cam gives the fastest throttle rate, smaller ones slow it down. This results in everything from a mildly-faster-than-stock 1/5-turn to a crazy-quick 1/8-turn, depending upon the bike application.
Installation on a 2009 Kawasaki ZX-6R took about three hours and a great deal of patience, due to a lack of instructions in the package or anywhere online. Removing and replacing the Kawi's throttle assembly with the aftermarket one was straightforward, but getting the cables on and off the throttle linkage, which is buried on the throttle bodies, took some work. The following pieces (as well as the electronics and fuel hoses attached to them) required removal: seat, side panels, fuel tank, airbox, right-side lower fairing and rear-brake reservoir. In the end, Euroracing's throttle tube needed to be shortened so the stock bar-end would fit properly.
To experience the greatest contrast with the stock 1/4-turn setup, the gold (fastest-opening) cam was installed. Now, the ZX-6R's throttle took just 12mm to open completely - a nice, fast 1/8-turn.
A track day operated by Sportbike Track Time at Monticello Motor Club, in Monticello, New York, was used for testing - and what a difference a 1/8-turn makes! The first thing noticed was a decreased amount of elbow movement needed to open the throttle, allowing the rider to be smoother and upset the chassis less. With its well-sorted fuel injection, the ZX-6R responded well to this super-quick-turn setup, never feeling too sensitive.
The Euroracing unit's quicker action also prompts riders to be smoother and more fluid with throttle input - thereby helping them to get on the gas earlier, accelerate quicker and attain full throttle with less effort - just the thing for track-day demons and racers looking for an edge. - Eric Putter
Quick-Turn Adjustable Throttle