I found the easiest way to adjust/check the tensioner was:
Mine was only rattling when cold, the noise went when the engine was hot. If yours is rattling all the time then you may need a new chain or tensioner.
Undo carbs and slide back and lift them up, you should have enough room to get to the tensioner out. when i did mine i did not disconnect the throttler cables.
Undo and take out the centre bolt in the tensioner, be careful as there is a spring and ball bearing in there, then undo the 2 mounting hex bolts. The idea of removing the centre bolt first is so when you remove the tensioner you can see how many more clicks/teeth are still available.
I had about another 4 or 5 clicks remaining on my tensioner when i remove it.
Make sure you replace the gasket with a new one or some silicone gasket stuff, i also replaced the copper washer to make sure i had no possible oil leaks.
To refit i reset the tesioner, refitted the body but left out the centre bolt, i then put the bike in gear and turn the rear wheel backwards just by hand in order to put all the slack on the tensioner side, i then poked a screw driver down the centre bolt hole and pushed out the tensioner until it stopped. Do not push too hard.
I then refitted the centre bolt and refitted all the carbs, air filter, fuel tank etc etc.
Once i started my bike up it was quiet, and lasted all of about 200 miles before it started to rattle again
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I now live with it and should it start to rattle when hot then i will replace the chain.
This is how i adjusted mine, but i'm sure other people might have other suggestions.
This is all done at yourt own risk!!
Mark.