How do you adjust the chain on your 1999 Honda trx 300 ex?

As far as adjusting the chain goes, to the right of the rear sprocket there will be a large concentric adjuster with slots in it. You'll have to loosen the two 6mm Allen head bolts on the swingarm just to the right of the adjuster. Then use a small wrench [turned sideways] and slip it in the slots of the concentric adjuster. If you push it forward, the chain gets loose. If you pull it back, the chain gets tight. You want to have about about 1 1/2" of play [up and down slack] in it when finished.

Then tighten the Allen head bolts and you're ready to go !!