Thanks for the responses, bertsmobile1 and logan01.
The machine may have sat for a while with stale fuel in it, and the first few times I ran it I used untreated gas/oil mix (until I smartened up). So ethanol is probably the culprit.
One follow up question for logan01: you said to make sure the air filter and choke are "good to go". Air filter looks good, what should I check on the choke?
Like I said, I'm pretty new to this..
Thanks.