^ Why? If the exhaust is completely off it could very well be an issue. My bike (4-1 header and a 5" exit on a long megaphone) will fire up with the baffle out but it won't stay running unless I give it a bunch of throttle or open the choke quite a bit. Same thing happened with my truck the other weekend when we had the exhaust off. Fired up but only idles for 10sec or so without the throttle and choke pulled. That right there is "low back pressure as the culprit"
However, I do agree that with a proper exhaust system in place, even one that has a sizable leak or decent length pipes but no mufflers, back pressure is rarely an issue.
