did the cop have a decibel meter,if not you can beat it
This is the key. Over here in Spain laws may be different, and the word of a law enforment officer is "presumed right", but only when it comes to things like you were passing on a straight line or talking on the cell phone while driving, or you had a blown light. For things like loud pipes, it's not their opinion what counts, but what a calibrated measuring device tell.
Furthermore, over here, when a vehicle is authorized to be sold because it complies with the driving regulations, if new and more strict regulations are enacted the old vehicles doesn't have to comply with them. Thus, if your CB350 complied with the regulations in the 1970's, it doesn't have to comply with today's regulations, be it sound, engine breather going to the air instead the airbox etc. For example, seat belts were not mandatory on the back seats until 15 years ago or so. Therefore, if your car was built before then, you can't be fined for not using the seatbelts -that you don't have in first place-
Raul