Fourth generation (since 2008)

In 2008, Kawasaki gave the EX250 its most thorough modernization in many years. The EX250-J model is known as the Ninja 250R worldwide. Kawasaki increased the MSRP by $500 U.S.D., to $3,499 in 2008, by an additional $500 U.S.D. to $3,999 in 2009, and a further $300 to $4299 for the 2010 model year.

Parts from the third generation are still found on the -J, but its redesigned exterior panels bring the smallest Ninja's appearance out of the '90s and into line with late-2000s sportbikes. The engine and drivetrain retain 30% of the -F model's parts, according to Kawasaki literature. The engine's compression and maximum torque have been lowered to provide better midrange performance, where the motorcycle spends most of its time. The redesign of the engine was a response to frustration felt by new riders, according to Kawasaki, resulting in improvements in engine response at low RPM, and making the bike smoother and "much easier to ride."^[10] Though the previous generation Ninja 250 had one more peak horsepower, or five more peak engine horsepower according to official Kawasaki specifications ^[8][11], according to testing by Motorcycle Consumer News,^[12] the new version's 20 or 30 percent increase in mid-range power allows the bike to pull from 3,000 rpm where previously it had to be revved to 4,000.^[4] The U.S.-spec -J model uses dual carburetors like the -F model, but the European-spec and Thailand-spec model have a fuel-injection system. The wheels were increased in size to 17", the front suspension was beefed up, and the front brake rotors were replaced with a larger "petal" design. A fuel gauge was put in place of the previous models temperature gauge. With the additional and redesigned equipment, the EX250-J suffered a ten kilo increase in wet weight over its predecessors.