One thing to note is that if you are doing a 4 banger (like a Go Devil engine) there will be a NORMAL 1-2 inch 'bounce'.. for any 4 banger. With only 4 intake valves there is a significant 'dead zone' between intakes opening.
Most of the vacuum videos/sites seem to center on 6-8cyl engines. If you have have a 4 cyl you *will* get a rapid, steady bounce only at idle.
I was so impressed w/how vaccum tuneing improved my 216 that I utilized it on my 72 Karmann Ghia w/a stock 1600cc dual port boxer engine and the readings, settings and operation was basically the same as with the inline 6. It improved that boxer 4 engine just like it did the inline 6. Perhaps inline 4's exhibit this bounce, as I didn't see it w/the boxer 4.
Dave
