2004 Official factory service manual for Yamaha YFZ450S ATV Quad., Page 312Get this manual
IGNITION SYSTEM EBS01045 EBS01044
TROUBLESHOOTING The ignition system fails to operate (no spark or intermittent spark)Check: 1fuse 2battery 3spark plug 4ignition spark gap 5ignition coil resistance 6main switch 7engine stop switch 8throttle switch 9carburetor switch 10.pickup coil resistance 11.wiring connections (of the entire ignition system) NOTE: Before troubleshooting, remove the following part(s): 1seat 2fuel tank cover 3side covers (left and light) 4fuel tank 5front fender Troubleshoot with the following special tool(s)2Battery Check the condition of the batteryRefer to "CHECKING AND CHARGING THE BATTERY" in chapter 3Minimum open-circuit voltage 12.8 or more at 20 (68 F) Is the battery OK? YES NO Clean the battery terminals Recharge or replace the batteryEBS01032