650 isn't too bad 600 is better. I take it your 318 is stock? Did everything work good before? Any changes besides the carb. Again it could depend...did you completely rebuild the carb. Is your dist in good shape (bearings good). Is it same when cold/hot. Do you get a puff of black smoke out the pipes?
Now I just pulled this chart and it looks like your running a #18 in the high end jet which could be giving you a over rich mixture or give you flood conditions