What's the redline of my bike's engine?
Kawasaki has actually changed the redline of the Ninja 250 over the production years. It's one of the few things which has changed.
Two things have actually changed. First, the marked redline (the red hashed area on the tachometer) has recently changed. In the 2005 model year, it made its first-ever change from 14,000 to 13,000. The second thing which has changed is the built into the .
The rev limiter is a circuit in the ignition which cuts out the spark to one cylinder once a particular RPM has been reached. Running on one cylinder, the engine is incapable of exceeding this RPM, making it a very effective method of keeping you from surpassing the engine's design limits.
The point at which the IC igniter begins cutting spark, by year:
The reason the rev limiter cutoff has been dropping is that Kawasaki has discovered that at the upper limits of the RPM range, the lubrication system may not be able to supply enough oil to some parts of the engine.
Fortunately, this doesn't represent too much of a performance dropoff, as the engine's power wanes considerably past about 13,000 RPM. The accepted point at which power ceases to increase is about 12,500 rpm. There's little reason to take the motor past 13k, even when shifting for maximum performance.