I'd make sure it's getting full throttle first, and if it is.......I'd see if I could borrow a different carb.
I'd be looking for a 750DP if it were me.

As long as the converter isn't broken/defective, and assuming there was a good carb on it, that combo should run pretty good.

I second the thought of doing a compression test on a least a couple cylinders, just so you know where it's at.