ATA 250E Chain tensioner, NEED BETTER

[Tonyrader]

I have two ATA 250 E and need a upgrade on chain tensioner, the stock one is sort of wimpy and crappy, any Ideas?
When the tech set it up I can see the axel is not square so that does not help, that is the first thing I will take care of, the other stuff like the adjustment og riding position of the clutch and other I need to do also, and a bathe for all rubber in armor all.. for a better UV stable rubber, hoping it doesn't rot out like the others, while its new before I put dirt all over them..

Also what's the deal with the E stop switch on the handle bars, you can flick it off then it returns to center, but its not on until you unflick it?
I need to see if the manual covers that,,, HUM,,,