We cannot possibly give you an answer based upon that little information.
Where is the cart? A high volume spot with full permissions? Or just a second spot he thinks will work?
Why isn't he working it? What are the profits?
What are the hours? What have sales been in that location?
Is this something you could just as well be doing on your own?
With a small business loan, could you set up your own cart and get ALL the profits after expenses?
Is this really what you want to do?
Being on your own means you have no one to turn to should something go wrong, and no one to help you. Being planted somewhere in the hot sun with a steaming cart full of valuable food isn't free money at all. It can be grueling, kill your feet and your back, and make you fairly sick if you're not up to it. I expect it also starts very early in the morning with a lot of preparation.
I have done similar things, and still remember how hard it was- and unprofitable.
You are better off looking into either less grueling forms of work, or ways to go into business on your own. If you are going to work that hard, you deserve to have a bigger stake in the business. Look at it this way- he would not be doing the work, and he would be getting 2/3 the profit- which is NOT what you collect every day- he would still be paying for the cart, the food and the fuel out of that- and your workman's comp and unemployment,because you would NOT be an independent subcontractor. Be careful- my guess is that he was going to try to make you that, too.
This is the sort of thing that sounds goods, until you do the math.
It is virtually always possible to go into business for yourself and make more money.
And if you wanted to try it, he would have you sign a contract roping you into doing it for longer than it took to find out it wasn't great. BE CAREFUL.