I have an Echo SRM-210 trimmer. Fuel is leaking through air filter leaving thick, oily residue after gas evaporates. Motor will start just fine, but I pretty much have to run it with throttle wide open to get it to keep running. If I allow it to idle, it dies. In order of priority, what steps should I take to fix this?

The little red primer bulb is on the side of the plastic piece that is attached to the carburetor . That piece holds the rectangular air filter . A second plastic piece attaches & clamps the air filter in place . I have to manually prime the lawn mower through the carb or spark plug hole . I have installed the red rubber bulb & a replacement carb . No joy . Is there a little " ball bearing " for a check valve , that I may / probably lost ? My understanding is the red rubber bulb forces sit into the carb bowl , pressurizing it . And this forces gas into the air path of the carb , priming it ? This is not happening on mine . Thanks , Wyr God bless