2005 Polaris Sportsman 400/500 Service Manual, Page 37Get this manual
MAINTENANCE
COMPRESSION TEST
NOTE: 4-Stroke 500 and 425 engines are equipped with an automatic decompressorCompression readings will vary in proportion to cranking speed during the testAverage compression (measured) is about 50-90 psi during compression testSmooth idle generally indicates good compressionLow engine compression is rarely factor in running condition problems above idle speedAbnormally high compression can be caused by decompressor malfunction, or worn or damaged exhaust cam lobesInspect camshaft and automatic decompression mechanism if compression is abnormally highA cylinder leakage test is the best indication of engine condition on models with automatic decompressionFollow manufacturer's instructions to perform cylinder leakage test(Never use high pressure leakage tester as crankshaft seals may dislodge and leak)Cylinder Compression Standard 50-90 PSI Cylinder Leakage Service Limit 10 (Inspect for cause if leakage exceeds 10)
SPARK PLUG
1Remove spark plug high tension leadClean plug area so no dirt and debris can fall into engine when plug is removed2Remove spark plug3Inspect electrodes for wear and carbon buildupLook for sharp outer edge with no rounding or erosion of the electrodes