My simplicity mower turns over fast when plug is out of the moter and it gets spark when I ground it to the mower. But when I put the spark plug back in the mower the moter turns over at a slow place. It is a new battery with 500 cca. Also it will get spark when plug is out of motor but when I put my thumb over the hole where plug screws in at it builds compression in motor and turns over at half the spped it will not spark.I can not figure it out.