That's quite right Dave, when i was a wee lad of 15 or 16, I bought a CZ 250 Motocrosser (well, they were called "Scramble" bikes back then) and with it's low slung expansion chamber and "stinger", my Dad (who wasn't a bike fan) would yell at me to "turn that bloody thing off", so I decided to quieten it down.
My Dad was/is an avid photographer, and back in those days rolls of film came in aluminum cannisters, and by chance, the can was a tight fit over the end of my stinger. I punched some holes in the end and it wasn't bad, then I stuffed some shredded "pink bat" bits in the end, and it was quiet.
I pushed it up to the old Bairnsdale racecourse where we were "kind of" allowed to ride our bikes without too much interference from the cops. Not having ridden it further than around my back yard, I was concious that this weapon of a bike was attracting some attention from the other kids, so I went for the big power takeoff...... and stalled it. Tried again, stalled again, bugger!
The previous owner, Ralph, wandered over and asked me what was wrong? He then noticed the "end baffle" I'd made, and told me to "take that fukking thing off", which I did. I then fired it up, and (to make up for my previous embarrassing performance) gave it the berries, dumped the clutch.......... and flipped it! Oh well, I did learn a valuable lesson about motorcycle exhaust theory and practise!