Originally Posted by jscottyk
Could the popping be related to the SAS that ebrabaek still has in place? Unburnt fuel plus extra 02 from the fresh air pumped into the exhaust plus heat equal combustion in the header? One of the main benefits the KTM crowd reports after the removal of their SAS is elimination of popping (backfires) on deceleration.
Also, it would seem the extra O2 in the exhaust provided by the SAS would provide an erroneous reading from the O2 sensor. Well, technically the sensor would be reading the O2 levels properly but the O2 levels would no longer be representative of what just happened inside the motor.
I suppose that the secondary air could be a contributor but doesn't seem like the primary cause. When exhaust components are changed, the flow is now into a system that has different resonances, leading to the possibilities that pressure vs rpm changes at the exhaust valves; and to the possibility that fresh air enters the exhaust system from the tailpipe and causing popping when it meets residual fuel.