Small Engines (Lawn Mowers, etc.): John Deere ZTRAK 737 zero turn radius mower

Question
Hello! 2 problems I have #1- accidental added approx 1 gal of gas/2cycle oil mix into mower. Problem didnt appear until third mowing afterward. Engine started to run ragged,spit&sputter,and backfire--but not stall. It sounded like not enough fuel. I figured the tainted gas was out of system by third mowing--so I added new gas,changed fuel filter, spark plugs,and both ignition coils(airgap set with new feeler gauges and bolts torqued to specs) then I added seam foam treatment to fuel tank to clean any thing out of fuel lines carb etc. Engine still sputtered as expected by addition of sea foam,but got better--so that for two mower ran almost perfect. Then last mowing I added fresh gas and some fuel stabil(fuel stablizer)to get mower ready for winter. Then is was worse than ever--not only backfired loud,but sputtered and actually stalled many times. It sound very much like not getting gas. Thats 1st problem.... 2nd problem i will put in another question!!! Thank you very much for your expert help!!!!!

Answer
I'd start by removing, dis-assembling and cleaning the carb with compressed air from an air compressor and spray can carburetor cleaner.

Newer carbs are very sensitive due to strict emissions controls.

I recently had to replace a carb on a JD...could not get the original carb to run right.  Customer was so mad about replacing the carb as the mower had very low hours on it he stated he wanted to sell it.  

Called him up to see if he had sold it or still wanted to sell it and he said it had never ran as good as after replacing the carb.  He said he loves the mower now and does not want to sell it.

Try cleaning the carb first.

Eric