My gas cart will not go in reverse

My gas cart will not go in reverse

I have a gas Cushman 1200X. It's a 2015 with only 40 very easy hrs. I doesn't want to go in reverse, ie; when I press on the gas gas the solenoid will click and try to back up but just will not quite go. On occasion it has kinda started the same in forward. Is there some adjustment on a belt or what?