2000-2005 Yamaha F40B Outboard Service Manual, Page 524Get this manual
TROUBLE SHOOTING FOR PEAK VOLTAGE
TROUBLE SHOOTING FOR PEAK VOLTAGE
Symptoms 2Unstable idling speed Unstable engine speed No firingThe starter motor cranks the engine, but no firing takes place in the cylinderFiring takes place in the cylinder, but the engine stops soonStart-up time is too longThe engine will not start-up easilyThe engine speed is not stable at idleThe engine stalls when the throttle lever is openedThe engine stalls after it is warmed-upThe engine does not run smoothlyThe engine speed drops during accelerationPoor starting
Check the ignition system1) Check the wire harness couplers to ignition coil, COl unit, pulser coil, and charge coil