I just want to back up Tom by saying that if you can get pass the fact that it sounds utterly ridiculous to most people, It really works!!! I have an older style head for a M2 and I used a smaller tube about 2" pvc pipe and I never heard the cylinder choke once the entire time. This simple mod saved us time, fuel, wear and tear, and headaches. I just wish I knew of this mod before. My two cents, Curt