In my opinion, partial throttle operation is OK for much of your operating time. When something is loaded, lugging -I assume that the heat would build to a higher degree than in a power blower application. If it were mine, I would be sure to use good oil plus to run at WOT at intermittent times to aid cooling and help clean the combustion chamber, screen and muffler.

Hello tomplum and thanks for your response. Appreciate it!

In a matter of fact, since I posted my question I already bought my blower (a PB-770) and ironically found the answer (or at least Echo's one) to my question in their user manual and posting it here in case it will be of use to someone else:
"Use reduced speed only when performing light-duty tasks or to comply with local noise regulations.Continuous low speed operation may allow fuel/oil residue to build-up on the piston and cause rapid build-upof carbon on the spark arrestor screen, resulting in overheating and engine damage. To reduce harmfulbuild-up, run engine at wide open throttle for at least 5 minutes every hour"

I can live with 5 minutes every hour... :-))))
Happy New Year!
JJ

Enjoy!