Lawn mower running suggish - Poulan "Poulan" Push Mower

I had the same problem Poulan 550 It would start fine, start getting slower and slower then stall. Then it would not start for about 30-40
minutes than same thing. I put and new plug (set the gap with my handy gage) then took off the air filter and sprayed carb cleaner right into the carb. bowl. Put it all back and same thing.
But while it was starting to slow down I had a screw driver with me and with the engine running i loosened the screw on the air leaner and the engine started to rev faster. loosened a little more and rev faster again. FInally pulled the air filter and finished the whole lawn
on one tank of gas. I cant believe the air filter can cause such an
issue. And the air filter looked clean. Time to try a new one

Fuel problem???? ya know carb cleaner works on lawn mowers as well as cars .