am in the process of tuning up the 550.  Replaced the ignition with the Genesse Products ignition 1 year or so ago along with the 12 volt conversion kit.

Wondering what heat range plugs people are using, and what gap they have settled in on.

NAPA book shows a D21 plug...had been running D16 Champions.  Genessee suggests no more than a 35 gap and Autolites.

any input would be appreciated.

Jeff