Engine won't run with air filter

I have 875 Briggs and Stratton on my  Lawn mower, engine number 121S07-0986-F1  This is a rear mounted  one.Problem I am having is that will not idle at corret rpms "low" with air cleaner housing installed on carberator. Out the housing RPMS sound fine , but when engage the blade it dies. This is carberator housing off. If you put air filter housing on with how the filter the RPMS go down and it seems to be bogging down. The throttle play is fully open at this point. I did just the governor air filter housing off, maybe RPM come up that sounds like correct rpms. Does anybody have an idea what this could i be?  I also put in a new flywheel key way.