Kawasaki’s Ninja 250R narrowly missed out on the win in this month’s 250cc sportbike shootout, which may come as a rude surprise to its many devotees. But with its off-idle roughness, paltry low-rev power and overly erect ergonomics, the “Ninjette” has some issues to address if it wants to regain its status as King of the Quarter-Liters. The littlest Ninja has been around for nearly three decades, and in that time numerous solutions to its shortcomings have been suggested by resourceful owners and the aftermarket. What could the bike become if we tapped into that vast storehouse of knowledge? We scoured the Web, determined the most sought-after upgrades and gave ourselves a $1500 budget to find out.
First order of business was dealing with the Ninja’s fussy off-idle engine behavior, Complaint #1 amongst owners of all skill levels. The problem is easily solved by adjusting the twin carburetors’ pilot air screws, a procedure that’s thoroughly documented on the Ninja 250 Riders Club forum (www.ninja250.org). Even better, it’s free!
While we had the carbs off, we decided to install Dynojet’s Stage II jet kit (part number 2139) in anticipation of an air filter and exhaust upgrade. The kit comes with several sets of larger main jets and replacement needles, as well as comprehensive installation and tuning instructions. Not sure what carburetor mods are best for your bike? The aforementioned forum’s wiki feature is an invaluable resource for curious owners and inexperienced DIYers.
With the fueling taken care of, it was time to add more air to optimize engine performance. With the bodywork removed to access the carbs, swapping the restrictive stock foam air filter for a high-flow cotton K&N unit was accomplished in under 5 minutes. One great thing about the Ninja is its simplicity, which makes it convenient for owners and aftermarket manufacturers to work on. Thus performance parts are surprisingly affordable and easy to install. A full Jardine RT-5 exhaust system cost less than a slip-on for a ZX-6R, and only took 30 minutes to bolt on. The carbon-canister system shaves off more than 9 lbs. compared to the ungainly stocker, and is perfectly sized to match the bike’s diminutive stature.
Strapped to our in-house SuperFlow dyno, the Ninja’s engine upgrades proved well worth the minimal investment in time and money. While peak output only rose by 1.7 horsepower (27.1 bhp @ 10,700 rpm vs. 25.4 bhp @ 11,100 rpm), power builds faster and is sustained longer. The modified bike reaches the stocker’s peak torque output 2900 rpm sooner, and there’s at least a 1-bhp gain from 6000 rpm on up, with a maximum difference of 4.2 bhp near redline where the stocker’s power falls off dramatically. That may not sound like much, but it’s a 20 percent improvement!
Out in the real world, the effects of the engine upgrades on rideability were impressive. The bike proved eager to start, required a fraction of the time to warm up and revved up off idle crisply. The power step at 6000 rpm was backfilled, and the midrange felt significantly fatter. With the throaty snarl from its Jardine exhaust and its extra top-end oomph, our modded Ninja begs to be caned. It’s a changed machine!
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