Turns out there is no air filter. Just a small plastic grill at the intake - photos attached. There also is no spark arrester screen - the entire muffler unit comes out as one piece (see photo). Air seems to go through the muffler assembly fine. And I tried starting the engine with the muffler detached - no-go.
It is getting spark (was running a month ago). The spark plug, fuel lines and fuel filter were new a year ago. The exhaust port has a very small amount of carbon, but is not blocked at all.
Any ideas? I THINK I did leave fuel in the tank all winter. Would this cause a clogged fuel filter?
Thanks.