Small Engines (Lawn Mowers, etc.): Engine problems, briggs stratton, head gaskets

Question
I have a Cub Cadet w/Briggs & Stratton 18hp V-twin Model #350447 Type 1206-E1 and under this is the no. 4952 Code 98011411.  (approx. 550 hrs) Engine was sputtering like low on fuel and smoke coming out of exhaust.  Friend took a peek.  Thought fuel was discharging from exhaust.  Cleaned needle valve on carb.  Also air filter was oil soaked.  Replaced filter and soaked again.  Replaced head gaskets and there was evidence of leakage.  
Air filter still getting oil soaked.  It is blowing up through that rubber tube.  When engine gets warm and/or under a load (mower blades engaged) ground speed reduces significantly. (I can walk faster than that.)  Have been adding some oil and gas consumption is higher.  I have 4 acres to mow like now.  Know this problem won't get better.  If I use it could I blow the engine?  Do I need to have it overhauled while is still runs or would it be cheaper to just replace the engine or buy another mower.  I paid 6k for this one 11 years ago.  Your advice will be greatly appreciated.

Answer
Hi Melanie
 Your needle valve needs to be replaced. Also be sure and check your crankcase because it is being over-filled with gas and oil. That is also why you are getting fluid soaked air filters. Make sure you drain the crankcase completely and put in fresh oil and filter after the needle valve is replaced. This should correct your problem. Unless it is burning oil, blue smoke from exhaust, you more than likely don't need an overhaul. Hope this helps.