Okay here is probably what going here as I have seen this a lot. [quite common issue] Either the air cleaner base is warped from heat or a heavy hand installer over torquing the mounting screws. Once warped is nearly impossible to get a good seal; unless, you make up a modified air cleaner base gasket.
Once you verify that it is not priming remove the new gasket and look that contact area of the primer air channel. Now using a second gasket shave it as to apply more in the non contact area and remove the un-needed gasket in the other areas. I usually bevel cut the second gasket and use light application of wood glue to hold in place until things are assembly as the pressure will bond the layers together later. May take a few test fits to get it right so don't glue until your know you got it right.
Now you might ask why not just use 2 full gaskets? Well I seen it tried and I have tried it too. It simply does work the same as beveled gasket setup.Thin one side and thick on the other.
Hopefully this makes sense.
