Small Engines (Lawn Mowers, etc.): Murray Garden Tractor spewing gas out the exhaust, gas seeps, briggs stratton

Question
My mom bought a Murray Garden Tractor 20 HP 5 speed in 2001.It has a BRIGGS & STRATTON 20 hp Twin engine (I/C Plus Model #460777 Type #2277E1 Code #0002155 B). It was running fine at the end of last summer. When her grandson went to move the mower, it started spewing gasoline from the exhaust. When my mom went to use it the other day, it again spewed gasoline from the exhaust. When she tried to find out what was wrong, she found gas in the oil. Any ideas what is causing this and what she needs to do about it?  

Answer
 Hello Kathy:

 I have Been Seeing this Problem a Lot Over the Past Couple of Years. From April Until October, the Shop will Service and Repair Approx 5 to 7 Riders a Week. Of these All have a Manual Cut Off Installed for this Problem and we Install a New Needle and Seat in the Carburetor if the Engine is Not Operating Properly. From Your Description it Sounds like the Mower is Working Fine Except for the Gas in the Oil Problem. This Means the Needle is Working for Engine Operation and When the Engine Sits is When the Gas Starts to Leak by the Needle and Fill Up the Crankcase with Gas. I Suggest you Install a Manual Cut Off Valve in the Gas Line to the Carburetor from the Gas Tank. The Needle in the Carburetor Isn't Seating Properly and allowing Gas to Leak Into the Carburetor and this Excess Gas then Flows through the Carburetor Throat to the Cylinder. Once in the Cylinder; the Gas Seeps by the Rings and Enters the Crankcase. Drain and Refill with Fresh Oil also. You can Replace the Needle and Seat in the Carburetor, However I have Found that Usually within 4 to 6 Weeks the Problem will Re-Occur if the Manual Shut Off Isn't Installed and Used Properly. There Seems to be a Manufacturing Problem with the Needle and Seats that are Being Use Today in the Carburetors. ALL the Engine OEMs are having this Problem, so Another Mower or Engine will Have the Same Problem Eventually. You should be Able to View a Breakdown/IPL of the Engine at this Addy http://www.outdoordistributors.com/ and Select the B. Then Select Briggs and Stratton. Then Select Don't have Part Numbers. Then Select the File #46. Then Select Folder Number 460700. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.

 Good Luck

 Respectfully

 John