After seeing many posts about these carbs not being tuneable I decided to try and help people out. I've had a 81' CM400 and another with a 82' 450 in it. I ran pods and a really less restrictive exhaust on the 400 and pods and open exhaust on the 2nd. I've had no problems with either one. The trick is simply swapping the main jets and raising the needle location with shims. I don't claim to be a carb guru or anything but i've tuned a few and never had any problems. I don't have any magical calculations I use,i just use the basic teachings I got from old hot rod guys. These engines really come alive once you open them up a lil and add some fuel. So in short feel free to let me know you're setup and i'll help you get her running great.