Re: how to make an engine quieter/stealth
Joe's mention of intake noise is important here. The pop-pop-pop sound that comes from the carburetor intake is often understated when talking about quieting the engine. As Barely Awake links, a remote air box, properly insulated and piped to the carb will go a long way in reducing the noise from your bike. I've experimented with several options and the one that works well for me is not only simple but also adds to the aesthetics of the air inlet. Rattle can, spray paint, can tops come in every color you can imagine. They can be installed easily with a long self tapping screw into the stock air cleaner housing. I wrap the inside with a thick felt that seems to absorb a lot of the pop-pops and it looks better than the black plastic air filter. Of course there are other options but give this a try. I'm not sure if spray paint comes in the same containers in Great Briton but any plastic can top that will fit over the air cleaner with space for padding will work.
Extending the exhaust pipe and installing the muffler at the end is always quieter than the kit pipe and muffler but requires some welding. Good luck. Let us know if you come up with anything new.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"