Small Engines (Lawn Mowers, etc.): craftsman tractor model 917.273170, tractor model, air leak

Question
Wont start backfires.  Cranks and cranks.
Kohler engine.  Ran fine two days ago.  Drained gas put new gas in same problem.  Spark plug A ok.  Filter(S) a ok
Did notice a bit low on oil. which I corrected.  Still no start
Help Please

Answer
Frank

If the machine won't start and the spark is good, you must make sure that fresh gasoline is getting to the carb. Make sure that the fuel shutoff valve (if present)  is opened, and that the fuel line is not plugged or kinked. Also be sure the fuel cap vent is open and any screens in the tank are clear of debris. If fuel can flow to the carb, carefully place 1 teaspoon of gasoline down the spark plug hole (or a add shot of starting fluid into the carb throat). Re-tighten the plug and try to start the machine. If it runs for a second or two, then quits, chances are the carb needs to be serviced (disassembled and cleaned & inspected, then rebuilt) or you have an air leak somewhere. Make sure all mounting screws or bolts are snug and gaskets are not missing sections. If the carb is a bowl-type check for water in the bottom of the bowl (but do not let the float swing all the way down or the float needle will fall out!).

Backfires thru carb or air filter: Intake valve not seating properly, check lash and/or reface valve & seat.