Small Engines (Lawn Mowers, etc.): picture diagram of murray Model 40507x8A riding lawn mower, riding lawn mower, 2 quarts

Question
need to change oil.  how much 30W oil to buy to replace and picture diagram of motor.  Oil Filter?  Just had new muffler put on and need to change oil.  Back-fired after two strips mowed.  motor is 12.5 HP, model 289V707, Code 991229ZD, Type 1113-E1  Thanks.

Answer
2 quarts will be more than enough Beverly.  And theres not an oil filter on your engine.  The back firing is a bit of a concern-  If you know a good shop- have them check your timing, and.....   ehhh - theres a valve that supposed to shut down the fuel when you switch the engine off from high RPM's (you didn't say when the backfiring is occuring)-what happens is the ignition is off, but the motor is still turning, fuel, unburnt, is drawn into a hot exhaust, where it ignites.  Lemme know about the backfiring ok?  When and under what conditions-
cya!