This worked well for me, how fast do you want to go?...
http://www.buggiesgonewild.com/sled-...-columbia.html
Taking the muffler off will make it sound faster, but won't help much in terms of speed. TO get more speed you need to take the jug off and grind the exhaust port timing to ~165 degrees. This will wake it up a little for an afternoons work.