Small Engines (Lawn Mowers, etc.): briggs carb overflow, engine failure, fuel inlet

Question
I have a briggs 17.5hp 31C707 overflowing gas into cylinder.  Have cleaned carb and replaced needle valve and float.  Can not blow air in inlet with carb upside down and valve seat looks clean.  No adjustment on plastic float.  Does have a solenoid holding bowl on.  I'm out of ideas.  Any help would be appreciated.  Thank you.

Answer
I hardly ever bother rebuilding either carburetor that comes with this engine.  The Nikki carb I always replace and the Walbro I replace at least half the time.  

You shouldn't try blowing air through the fuel inlet.  The test is to apply 7-10 pounds of vacuum and see if it will hold.  The metal part of the seat may be able to be polished to create a good seal.  If the float is sitting level when the carb is upside down, then that may cure the leak.

For my shop, the reason why we replace this carburetor is because the number one cause of catastrophic engine failure in this engine model is the carburetor leaking fuel into the crankcase.  We rebuild and replace dozens of these engines each season because of this failure.  Let me know if you have any questions.  Thanks, PK.