Small Engines (Lawn Mowers, etc.): Sears lawn Tractor wont start, minor bit, feul

Question
QUESTION: This past weekend I started my lawn tractor and it backfired, then immediately stopped.  I wouldn't start, not even turn over.  Gasoline was observed coming out of exhaust (dripping onto plate under engine).  When I attempted to start it (with hood raised) I noted the flywheel (?) move a minor bit but the engine wouldn't turn over.  Checked the oil, it was just above the add oil line.  Had no problems previously.  Lawn tractor is a sears, gray colored, 17.5 hp.  I have some (long ago) experience repairing small engines, but, where do I start (or is this serious enough for me to bring it in)?  Thanks much.

-Gary

ANSWER: Start by pulling the plug, cranking it over, and unloading the cylinder of fuel, it's is hydro-locked (too much liquid in the cylinder), thats why you oil is over full ( fuel passed by the rings), and the engine can't rotate. The back fire could have been the magneto failing. Check and see if you have spark. Chances are you lost your spark, then continued to try and start it, and flooded the cylinder full of fuel to the point it can't compress the mixture now.....Tom

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

QUESTION: Tom, first, thanks for the information.  I did as you directed and, after determining that I did have a spark, put everything back together and it started right up, although it runs a bit rough.  I emptied the oil and replaced it.

My question: would the roughness be due to the fact that maybe the oil isn't "pure oil" (some residue of gasoline), and if so, how do I make sure to get all the gasoline out of the oil?

Thanks again.

Answer
First off CHANGE the OIL, it has gas in it now, and isn't giving you good protection, it is contaminated, with feul. It could also not be giving you the best seal around the rings now for top compression. Second, your plug now may need replacing due to it getting contaminated. Your air filter maybe not letting enough air in if it is oil or gas soaked. Not to mention that coil may be weak, enough to run it, but not enough to run it correctly. Don't foget to rate these answers please.......Tom