Re: Drops off while running
why not test the trigger?<br /> the stator controls all 4 cylinders the trigger controls 4 but in pairs.<br /> the merc manual has a good description of how the Altenator Driven Ignition system works,ADI.<br /> the stator provides an AC voltage to the switchbox where its rectified to DC and stored in a capacitor. its just sitting there like a little bitty battery. the inner hub magnets on the flywheel control a pair of smaller coils called trigger coils. as the little magnets rotate creating a small AC voltage in the trigger coils that voltage is sent to the SCR that controls the discharge of the capacitor. once the SCR ,on the output side of the switchbox, is turned on the capacitor will discharge into the ign coil primary. the current creates a rapidly growing magnetic field in the primary windings of said coil.<br /> all of a sudden the cap is completly dischaged and no more current flows. now said magnetic field is rapidly collapsing and induces a very large volatge with very small current into the secondary coil windings. this voltage can exceed 20KV on that 40 but typically needs less than 8KV to jump the plug gap.<br /> so with a little understanding of how and why your system sparks coupled with a peak reading,NOT RMS, multimeter its a fairly easy straight fwd CDI ign system.<br /> without the knowledge or the test equipment it can be an expensive nightmare for the do it yourselfer.<br />nice thing about it is even though the component names and shapes change ALL capacitor discharge ign systems work with the same electrical rules, only the controls change.<br />so if you understad how your 40 HP system works you understand how yamha,evinrude,tohatsu and all the rest that use a CDI ign work.<br /> only the method of timing control chages and even then its all the same only the wire colors change.<br /> while its technically possible that your high speed windings are failing normal failure on that motor is low speed windings but we did have a lot of trigger/trigger wire failures. last stator I bought for that motor was a bit over 200 dollars and that was in the 90's, last trigger was about 170 and switchboxes are about 150.
