quote:Originally posted by JTpantera:
... However, I do not believe it is a lean condition in my case. I suspect that gaps in the 180s where the pipe slide together introduces air and ignites the residual fuel left over perhaps from scavenging.
...
Lean meaning lean exhaust gas mixture. Normally the exhaust gas is rich enough, or lacking enough oxygen to ignite. Introduce O2 from some source like a leaky gasket or pipe, and you have backfire.
Another option to induce backfire would be to tinker with the PCV valve or other full vacuum port. If you could add an rpm activated valve that would open when the throttle is closed and RPM is above idle, but close when the RPM is in the idle range, then you might be able to introduce O2 in the decel stage, but not mess up the idle.