From the middle of the 2 sprockets you should have about an inch of slack or play in your chain when you lift up on the bottom of the chain with your finger if it looks a lot more then that adjust it but you don't want it to be too tight.
You need to start by adjusting the middle chain . At the front of the center chain is an eccentric , loosen the two bolts and rotate it to tighten . should be as tight as you can get it . After you do the center then you do the front .There is an eccentric for the front chain also . It should be as tight as you can also .
You should be able to move the chain up and down aprox 1/2" with your fingers.
yfz450
it should have 1 inch to 3/4 inch slack in it
a stock yfz450 goes about 75 mph
they keep your chain tight
yfz450 nerf bars fit banshee
Half inch to an inch of slack in the middle is just right.
Don't know about quads, but here is a good thread on it: http://www.bluetraxx.com/forums/showthread.php?t=70861 Check the 3rd response down, that should tell you what you need to know.
You should be able to fit two fingers between the section where the chain touches the swingarm. It should not be crushing your fingers. Adjust the chain until it isn't too loose or smashing your fingers at all. Make sure to lubricate your chain before and after every ride
yfz450 is a Yamaha sport 4 wheeler 450cc engine a very powerful machine