Fun bike, Yamaha’s 2006 FZ1, a half-faired standard with a sit-up riding position, an excellent chassis and an R1-based motor that makes the bike a genuine bullet. On the right day under the right rider on the right backroad, a new “Fizzyone” can be just as hard to hang with as the R1 that spawned it.

But as many owners of an ’06 have reported, a couple of glitches in the EFI system’s fuel delivery can take the edge off the fun factor. The engine occasionally stumbles right off idle, and it consistently responds with a big hesitation when the twistgrip is turned open from trailing throttle. It’s almost like the engine stops firing for a fraction of a second then abruptly springs back into life, a characteristic that’s annoying in traffic and upsets the chassis when you’re trying to be smooth through the twisties. In our 2006 Ten Best Bikes balloting, that trait, more than any other, was the deciding factor that led us to select the Triumph Speed Triple as the year’s Best Standard rather than the FZ1.

Those injection quirks are caused by the lean air-fuel mixtures Yamaha employed to help the ’06 FZ1 meet the emissions requirements of all 50 states. The off-idle stumble is the result of leanness at small throttle openings, and the hesitation stems from the EFI completely shutting off the fuel delivery during trailing throttle and then restarting it once the throttle is reopened.

Aggravating, to be sure. But at least there’s an easy and not-terribly-expensive remedy available with the Fi2000R from Cobra Engineering (714/692-8180 www.fi2000r.com). This “digital fuel processor,” as Cobra calls it, plugs into the bike’s injector nozzles and alters the mixture by modifying the signals sent to the injectors by the Engine Control Unit. Beneath the processor’s flip-up cover are three adjuster screws, called “pots” –one for low-speed running, one for the midrange and a third for full-throttle/high-speed operation. The pots can only add fuel to the mixture, not subtract it – which is okay, since the mixture problems caused by stock EFI systems are brought about by leanness, not richness.

Cobra sells the Fi2000R for numerous late-model motorcycles, each one pre-adjusted for its intended application; so with a stock FZ1, you don’t have to do anything but hook it up and ride away. Just plug the Fi2000R’s four connectors between the injector nozzles and their original signal wires, attach the processor’s ground wire to the negative battery terminal, disconnect the wire that leads from the bike’s oxygen sensor and mount the unit under the passenger seat with a provided Velcro. Bingo! You’re finished.

Your reward for the $250 cost of the Fi2000R and the 15 or 20 minutes required for its installation is a much cleaner-running FZ1. Our dyno tests showed that the processor yielded no meaningful power gains, but it transformed the throttle response from sluggish and herky-jerky to crisp and smooth. The stumble off idle was history, and the hesitation upon reopening the throttle was non-existent the vast majority of the time. For reasons even Cobra cannot explain, that hesitation occasionally resurfaces; but even when it does reappear, it is so vastly reduced compared to stock that it’s practically not there.