340 No low end power

Not sure on the vaccum, no lines or advance at all. It is an aftermarket carb. Idle is at 900 and is rough, like a bigger cam would be. I have the stock dual plane intake but not opposed to buying a better one. I know its hard with the limited info I have but I dont want to start throwing parts at it. What seems weird to me is how sometimes it will burn them off but most of the time it seems like it has a rev limiter on it.