Hi Zoomy, and welcome to WF.
You didn't give the whole picture to answer your question. What prop are you using on the motor. It could be it's over-propped and pulling too many amps now. I have no idea how much you know about these kind of electronics, but the prop you put on the motor has a huge effect on it's amp draw, so while it may have been fine with the stock Radian folding blade prop, I bet you didn't use that prop for the hovercraft.