The exhaust gas temperature on a gas engine runs between 1100 and 1400 degrees depending on how you have the carb mixture set. Most rubber products will not resist this temp., or not for long. You need to find some silicone tubing for an exhaust hookup. That's what the model engines with tuned pipes use. Lightweight metal tubing will almost certainly fracture from the vibration.

Hope this helps,
AV8TOR