Vacuum Spring Problem?

I would do a couple of things, if it were me. First, get your hands on a 318 port sized intake. A dual plane, take your pick, just so long it's for the 318 size port. I'd also replace the heads before I had port work done. I'd swap on a set of "302" 318 heads. They are a closed chamber, with much ports much better suited to torque from a smaller engine. A cam, the stock 340 would work, but I'd probably go for a small Comp Extreme Energy. The XE256H would be #1 choice. But, I think by careful tuning, you can get it to run ok the way it is. Maybe not the best, but certainly not so bad it cant run well.
You may also, as it was said, want to check the float levels and pressure, just to be sure.