When throttling down my engine, unless I do it particularly slowly, it will give a single pop very loudly from the exhaust. It will also do this if I shut it down from a low idle speed. I read something about the idle circuit continuing to draw gas into the exahust stream on shut down, but this doesn't seem to explain why it also happens on a normal or rapid throttle down. The plugs are still running, so why the pop?
Rapid throttle down causes a backpressure in the muffler and the in rush of air ignites the unburnt fuel vapors in the mufffler, same as it does when shut off at idle.
