we have found the 280 to ber very clean burning after checking the ports this winter after a full season, none had carbon buildup compared to the 311 which had some and just a little is enough to slow the engine down so you dont get the raw power it can produce. just an observation i have had.
we use opti 2 cycle oil and it has made the difference, b4 on the 311 with other oils we would clean the ports about 4 times a year. now once, maybe twice on an older trimmer. we change plugs and air filters once every month, air filters as often as needed though and sometimes that is twice per month depending.