Vacu-Jet issue

I installed a rebuild kit into an Vacu-Jet carburetor on an old Briggs engine on a lawnmower (Briggs model/type 092502-3104-01).   It starts and runs nicely if the mower is stationary, but if the mower is moved back and forth the engine floods as if the sloshing fuel is getting sucked into the intake somehow.  Don't see any cracks in the plastic carburetor body or tank and don't see anything wrong with the diaphragm.  Any thoughts?

SRTsFZ6
You do have the main air filter screw installed, part  #584 installed, correct?
 
 
 
That not installed, will allow fuel to slosh up into the intake.
 
 
Thanks for the response - Yes, that screw (I believe you mean part # 534)  is installed and tightened properly, and I did notice that the hole for that screw goes completely through the carburetor body and into the tank, so yes, if the screw is not installed, it definitely would allow fuel to slosh up and be sucked into the intake.  I'm beginning to suspect that the diaphragm isn't sealing properly between the carb body and the tank.  I do see fuel traces on the diaphragm when the carb is removed from the tank.  I think I might try to cobble up a thin soft gasket to supplement what the diaphragm is supposed to seal.  Not sure what else could be permitting fuel to flood the carburetor when the mower is being moved back and forth....