Do i really need the tensioner on my motorized bicycle?

Cut a few links out and move that tensioner forward.

I'd only take one outer and one inner link out. Where you have it right now the tubing looks too small for the clamp. So when you move it forward see if that tighten it up some. If not then get some 1/2 inch tubing cut off a piece about 1 1/2 inches long then cut a slit into the tubing so you can fit it over the bikes tubing. Cut the slit wide enough to where there's about 1/16 inch gap after you put it on the bikes tube. Then see if the clamp tighten down good on that. If it does remove enough paint off the bike's tube for the sleeve. Put a little metal bonding epoxy on the bike tube then put the sleeve on it. Then wipe any excess off and use the tensioner clamp to help squeeze it tight. Let it set up for a day. On the clamp itself be sure to use teflon nuts on the bolts. Also make sure the chain is in a straight line. You can go to motorbicycling.com and motoredbikes.com for help.