I tried to keep the plug in place with the 2 piano wires that can be seen in the picture. That was not enough so I added a threaded rod with 2 long nuts. I just expand it inside the pipe so it can't move. So far it seems to stay in place.
It is also important to decrease the sound from the inlet which can be substantial.
The person doing the test is not a government employee. He is a member of a non profit organization of inspectors for this kind of vehicles. The inspectors are usually experienced builders of cars.
For the next try I have the Al discs on the wire, 6 steel wool balls, and the plug made from expanded metal in each pipe. I have also disconnected the second stage on my carburetor. I really hope this will be enough!
