The other thing to look at is what type/brand of 2cycle oil are you using? My recommendation is to match the 2 cycle oil to brand name on the unit. In my job we have to run a series of emissions tests on the units we normally get better results following the above.
As for the comment on removing the spark arrestor and throwing it away, In my job I can not even suggest doing that without getting trouble, take that with a grain of salt and do it either way.