I also have an Echo chainsaw, the manufacturer recommend a specific 'octane' rating, just as they do in my Johnstone 2st outboard (92) normal regular fuel with 100/1 mix for the outboard with special oil
the chainsaw has done only 6 hours work, (will sell it)
so I don't remember the tech specs for it but it uses different oil, as one's water cooled other air cooled.