I have a 2000 Kawasaki 900 STX. I just put a new motor in it. It ran good a few weeks then it started running slow. Checked plugs and the rear one was loose. I tightened it up and still slow. I checked spark and the rear cylinder had no spark. I changed plugs, the wire and ignition coil, and the CDI box. I still have no spark on the rear cylinder. Any ideas what I can check next? Front two have spark just not the rear.

Thank you

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