noise on engine sprocket


last month I had a flat on rear tire, busa -05- I got it fix and put the tire back on . after a week I start to get a clocking noise from engine sprocket area when the chain is picking of speed my guess is chain wos too stretched and damaged the eng.sprocket . * hope is just that * Right now is (17T original ).
any recommendations on replaced number ? 14 ,15,16,17,or 18 ... any one

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am going by the dots on the chain adjustment on rear tire, i even give some slack on the chain the noise is less but still have some noise.