Small Engines (Lawn Mowers, etc.): Briggs 21.5 intek Backfires, craftsman riding mower, filter air filters

Question
QUESTION: I have a craftsman riding mower with a 21.5 Briggs Intec. The problem I'm having is that the engine starts to back fire when the blades are no engaged. This will start only minutes after starting up the engine. I have changed the spark plugs, fuel filter, air filters, run the engine with the fuel cap off. But, the backfiring continues. There doesn't seen to be any lose of power. When the blades are engaged the backfiring stops.
ANSWER: Hello Kenneth:

Send me the Model Numbers Off the Mower, Please. With these I can Locate the Proper Manuals and Better Assist you. However, A Faulty Safety Switch, a Bad Coil, Improper Air Mixture or A Damaged Flywheel Key are a Few of the Causes for this Problem. Hope this Helps.

Respectfully

John

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

QUESTION: Hi John,
The model number for the tractor is 917.272464 and for the engine YBSXS 7242VF  274844
I hope this helps

Thanks

Ken

Answer
Hello Again Kenneth:

Thanks for the Information. Check the Safety Interlock. Try Bypassing the Safety Switches, One at a Time. I have Not Seen or had this Problem in the Shop Before. Since it Only Does it when the Blades are Disengaged and Not when the Blades Are Engaged; A Safety Switch May be Shorting Inside the Switch Due to Engine Vibration. You can View a Breakdown/IPL of this Mower at this Addy, http://www3.sears.com/. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.

Good Luck

Respectfully

John