Hey Chris, check the rubber valves and boots on the back of the vacuum canisters. If they are torn, you'll get the "lazy eye" syndrome. Spray some lubricant around the area and start her up. If you see bubbles forming, you found the leak. Good luck.--Bullitt
As well as that you might want to check the in-line vacuum filter.
It might have collapsed and blocked the line. Check that one of the lines isn't pinched either as that will cause problems.
To do away with all of the above just replace all the rubber vacuum lines with stainless steel tubing like I did. Works great and looks much better too.