It's probably an electrical problem - but I do like the idea of trying a carb. that you know is good. That's a really good way of eliminating a lot of potential problems. As far as vacuum testing is concerned, it helps to know where your engine ran when it was running well. In any case, you can find LOTS of info. on-line concerning vacuum testing. Check out:
http://www.atlanticz.ca/zclub/techtips/vacuum/
Looks like some good info. there.