Hi Chris
I had the exact same problem recently i found that if you take the bottom casing of the hedgecutter where the blades are attached to the engine. On mine, the top blade was not turning with the engine so the whole thing was moving together at the same time, like yours. I had to bend the end of the blade down a bit to make it catch and it has worked ever since. An easy way to check it is to put a cordless drill on the shaft to turn the engine and this allows you to see if the blades are moving correctly.
hope this helps.
Glen, August 2008