Hmmm, normally in the papers, there is mentioned the " old" measure procedure, if I remember correctly 71 dB(N)  for my DT250 and DT400. There are existing, according to procedure, dB(A), dB(N), dB (P) depending on the Date of first registration of the bike. For the " translation " into recent modern DB measurement procedure, 21 dB globally are added to dB(N), at least in European Union = 92 dB.  Maybe Switzerland has something similar,  so you are not far away. 

Hoi Guido,the Swiss regulation have a limit of 82 dB(A). I've been looking on homologations of old bikes, like Suzuki T500, Yamaha DT2, KAwasaki H2 750 and they are all below 82 dB(A).Most likely they were modifyHoi Guido,the Swiss regulation have a limit of 82 dB(A). I've been looking on homologations of old bikes, like Suzuki T500, Yamaha DT2, KAwasaki H2 750 and they are all below 82 dB(A).Most likely they were modifying them for the inport, has it has been later with the emissions as Switzerland had its own stricter rules.So I've decided to modify the bike as well as follow:  



I've used the one with the bigger hole, some high temperature on both sides as it's not a very soft copper. Let's say the bike should pass now.

As written, the method is the key.
-distance and angle of the microphone
- revs
-gear
speed (or still standing)
All this will influence the result.
Austria (Tyrol) has the strictest limits, 92dB(A), standing bike. Even the police over there was not allowed to use their own Police-bikes, as too loud.
I can not imagine 82.
As the bike is from 1975, they have to refer to limits, valid in 1975.
Something at the Traffic department went completely wrong. Is there another one in a neighbor city, you could ask?
Or ask at your ASC (Automobil Club Switzerland)

Yes, you are right.

I think the guy today didn't even do the sound check as someone in the background said that the measuring instrument/room was out of order.

He check the whole bike, rode it around and we managed to get a Swiss number plate on it!

Thanks everyone for the inputs, especially the one about the stuff in the air intake, it took away a lot of the noise.

"He check the whole bike, rode it around and we managed to get a Swiss number plate on it!"

"I think the guy today didn't even do the sound check as someone in the background said that the measuring instrument/room was out of order."

Loudness clearly not THAT important, then!