We need to see some pictures of what you have but Chaz is correct. Tension should be applied to the lower chain run, not the top. The top chain run is already under tension as it drives the bike. That's not where you want to apply pressure.
Contrary to what I posted in this thread back in 2010, I have come to find that spring tensioners have no place on a motorized bicycle. A tensioner needs to be adjustable, but not by spring pressure. Because we are dealing with acceleration and deceleration forces on a bike a spring tensioner will flex and allow slack when you least want it. On industrial applications you might see a spring loaded chain tensioner but those drive systems only drive in one direction and do not decelerate as you'll see on a bike when you release the throttle at speed.
If you can run without a tensioner, that's the best approach. But if your bike frame does not allow it the best way is to mount the tensioner so it spans the seat and chain stays and applies pressure to the bottom chain run maintaining 1/2 to 3/4" of slack.
Proper sprocket alignment is also critical. The tensioner is not a chain guide. It should not be used to apply side forces to the chain to get it to engage the sprocket or to clear the frame.
Tom
