Small Engines (Lawn Mowers, etc.): John Deere Sabre 1438HS, briggs stratton, engine oil

Question
QUESTION: Hi Eric,
I have a John Deere Sabre 1438HS (Briggs engine)with a problem.
It's been a great little mower over the years for trimming with no problems. Recently, it appears that gas is getting into the muffler. I am reluctant to use it. Could it be a bad valve & maybe consider replacing the engine. It ran great before this started. Other than this problem, the tractor is like new.
Thanks for your inputs.
Gary A.

ANSWER: Has the carburetor inlet needle and seat ever been replaced?  It is pretty common for the inlet needles or the seat to leak allowing gas to enter the engine oil.  This gas thins the oil which finds it's way out the muffler.

Does the oil smell like gas?  

Eric

---------- FOLLOW-UP ----------

QUESTION: Hi again Eric,
Thanks for your prompt reply. You mentioned the carburetor, seems my son changed it with a new one about a year ago. Don't know why.          It was purchased from 'Small Engine Supplies'.
Briggs & Stratton p/n: 791886. Maybe an adjustment is necessary.
I'll try adjusting and hopefully the problem will go away!

Thanks Again Eric,  
Gary A.

Answer
Does the engine oil smell like gasoline?  Is the engine oil too high or too full?

If you answer yes to either of these questions then most likely the carburetor inlet needle/seat is leaking.  Very common problem these days.  

If the oil smells like gas you need to change and re-fill with new oil to avoid major engine damage.

Eric