If your tensioner is maxed out then its time for a chain, you won't do anything but cause damage or continue to have timing issues until you replace it.
You can replace the chain only with out having to pull the motor or top end on the 200ES, i have done it, its tricky but doable. Chances are if your chain is that sloppy though then you need to tear down the top end, new chain, new tensioner and guide for it, and at the minimum a top end gasket set and a left case cover gasket. Its almost cheaper to buy a full engine gasket set and then you have what you need plus the rest for maintenance.
Once the chain is replaced you just line up the cam and crank and your done.
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1984 Honda ATC200ES "Big Red"
1982 ATC200E "Hondie"
1988 TRX300FW "Project Quad" Still in progress....