Kawasaki Ninja rough idle: throttle body sync and air leaks
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Applies to: Kawasaki Ninja 400, ZX-6R, ZX-10R and other multi-throttle-body bikes
Symptoms
- Lumpy, uneven idle
- Vibration at low RPM
- Snatchy throttle response
Why it happens
The throttle bodies drift out of balance, or a cracked vacuum line or intake boot leaks air into one cylinder.
How to fix it
- Inspect vacuum hoses and intake boots for cracks.
- Warm the engine and connect vacuum gauges to each throttle body.
- Balance the throttle bodies with the adjusting screws per the manual.
- Set idle speed to spec.
Tools and parts
- Vacuum gauge set or synchronizer
- Vacuum hose
What the factory service manual covers
Fuel system: throttle body synchronization, idle spec, vacuum routing. The full procedure, specs and wiring diagrams are in the factory service manual for your machine.