Thanks for the reply. I saw that youtube video of how the British guys takes apart the bayonet. From watching this, I found out that my Karcher adaptor didn't come with the inner tube or O-ring. I am going to give AG a call since I just got in my foam cannon 3 days ago.
I am having the same issue with new AG Foam Cannon HP. I have a Karcher K2.38 1600 psi and it has a lot back pressure from the plastic Karcher attachment. This is causing hardly any pressure for the cannon to work properly. I hope there is a solution for this. I just got the foam cannon 2 days ago.