I was concerned earlier when I had checked than while cranking with the starter, and it was hard to getting more than 1/8” jump.  Have no problems starting, but it seems the output is quite sensitive to voltage; and may be among the first reasons for loss of power following an alternator failure.

 

I guess I have D580’s, but I don’t know what the difference is from a D581.

 

Al G

The low cranking voltage is common due to the high current draw of the starter. Put an Amp Probe around the starter wire or a volt meter on the battery during cranking. The poor performance of the coil is cured as soon as the starter circuit opens. Ignition coils should work down to fairly low battery voltage, should the alternator fail. The controller may shut down first. Ignition performance that is being reduced by a dying battery may be extended by reducing throttle. One factor in secondary ignition performance is cylinder pressure. A badly missing engine from low voltage may return to power with just a slight reduction in throttle.

(reduces cylinder pressure).

 

Lynn E. Hanover