Small Engines (Lawn Mowers, etc.): Craftsman riding mower, information thanks, spark plug

Question
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Followup To
Question -
Hi Marc,
 Recenty we replaced the blades and belts on our riding mower. Since then whenever we start to cut grass the motor is running ok but the blades slow down when they touch the grass. The oil has been changed also the filter and spark plug. Its a 12.5hp
42" deck. Please let me know if you have any suggestions thank you
         Paty
Answer -
Do you mean the engine bogs down or the engine maintains RPM and the blades just don't cut?  The reason I ask is because I need to know if the engine is losing power under load or something in the blade drive is slipping.  Please write back with this information....thanks.

Marc the engine does maintain RPM, but the blades slow down when I begin cutting.  Paty

Answer
First I'd check that you routed the drive belt(s) correctly.  Then check the tensioner(s) to make sure the belt is tight when the blades are engaged.  I'd also make sure that, if equipped, the blade brakes are disengaging properly when the blades are engaged.  Hope this helps.