When I was a kid, I liked to play around with weedwacker engines. I'd remove the plastic caps that limited movement on the low and high speed needles and lean the hell out of them on the high end so that they would just scream when you floored it. One became useless as a weedeater because the handle vibrated at such a high frequency it made your hand go numb almost instantly.
It was probably hell on the motors but they were free!
On top of that, I would take a punch to the mufflers and poke as many holes in them as I could. They might as well have had a straight open pipe attached. Definitely wasn't doing my hearing any favors.
Nathan