Pedals, motor mount, ribbed plastic tube over axle, disc brake all point to a Manco kart, or its several company-name variations: American Sportworks or American Landmaster as they are now known. Never seen a kart quite like this one. You can usually trace the lineage on a frame design as newer and newer karts are just a rehash of an older frame design.
I'm just baffled that it has no suspension whatsoever. Going on that, it's far from ideal for offroading and the brush guard/roll bar becomes superfluous. My personal philosophy is that unneeded parts should be removed. I'd turn it into a parking lot racer (pavement) or use it on dirt/gravel roads.