Small Engines (Lawn Mowers, etc.): 20hp briggs ohv sears craftsman mower, sears craftsman, ohv engine

Question
I have a brand new (less than 1 hour) and when I engage the blades, the engine backfires and misses.  I have a hilly yard and it seems that the miss is worse when I'm going up hill.  The mower is a craftsman YS4500 with a briggs intek gold 20 hp ohv engine.

Answer
 Hello Greg:

 From your Description it Sounds like the Carburetor is Out of Adjustment. If it is New, I Suggest you have Sears Repair it. However, Send me the Sears Model Numbers(502.xxxxxx), Please. With these I May be Able to Locate a Breakdown/IPL and Better Assist you. If the Carburetor has a Fuel Shutoff Solenoid; this can be the Problem Also. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.

 Good Luck

 Respectfully

 John