Only way to get to the air filter on a Boliy generator is remove the two side panels (4 screws each) and the rear engine cover by removing two rear bolts (13mm Head) on the carry handles, some screws on the bottom rear (I think 6), and 4 inside screws ( 2 on each end that connect to the rear cover).
The air cleaner is directly behind the battery, held in place by two 10 mm head bolts...It has a washable foam filter.