What compression readings should I expect on a 2007 Kawasaki Ultra X supercharged engine?

If you mean the 2007 Kawasaki Jet Ski Ultra 250X, expect roughly 120 to 180 psi (8.3 to 12.4 bar) when testing cranking compression on its stock 1,498 cc supercharged engine, though this is a working guide, not a verified factory acceptance range. All four cylinders should read close together, ideally within about 10%; check the test conditions before deciding the engine needs repairs.

Confirm the model

The 2007 supercharged model is normally the Ultra 250X; the naturally aspirated Ultra LX has different engine specifications. Check the identification plate and establish whether replacement pistons, camshafts or other internal modifications have been fitted before comparing figures.

A compression gauge measures the pressure developed as the starter turns the engine. It does not measure supercharger boost, and you cannot convert the engine's compression ratio directly into psi.

Battery condition, cranking speed, engine temperature, throttle opening and the gauge itself affect the result. Four similar readings at the lower end call for a controlled repeat test before a strip-down. Three strong readings and one distinctly weak cylinder need closer investigation.

Get four comparable readings

Use a screw-in petrol-engine compression tester with the correct spark-plug thread adaptor and a sealing washer. Choose a tester with its non-return valve close to the adaptor: excess hose volume can give misleadingly low readings.

Ventilate the engine compartment and disable fuel injection and ignition using the model's workshop procedure before cranking. Keep sparks away from fuel vapour.

1. Charge the battery fully. Slow or progressively slower cranking can make the later cylinders appear worse.
2. If the engine runs safely, bring it to normal operating temperature using the correct operating and cooling procedure. Record whether the test is warm or cold.
3. Clean around the plug wells, then remove all four spark plugs so the starter turns the engine consistently.
4. Set the throttle opening as specified for the compression test. A closed throttle restricts incoming air and can lower the readings.
5. Fit the gauge to the first cylinder and crank until the reading stops rising. Use short bursts within the starter's duty limits.
6. Record the pressure, release the gauge and repeat on the remaining cylinders under the same conditions.

Check the adaptor seal and repeat any surprising result. Note the test order and battery condition, especially when comparing results from different days or gauges.