^+1 Don't worry about the jump. It's supposed to do that. The timing will always rev back to your base timing you set it at. So if your base timing is 12 degrees with the ECU advance disconnected, when you plug it back and hit it with the timing light again you'll notice the timing change because of the ECU advance.
Depending on what the ECU picks up will determine how much advance to get a better burn during idle. Make sense?

B.Y.E. ~ Back Yard Engineering