The ignition timing and fuel mixture would be a very good place to start. Is the throttle closing off, back to idle, or hanging open slightly?
Phil Matheson SAAA Ch 20 http://www.philskr2.50megs.com/
- KR> Backfiring at idle/slow speeds Neal Hornung
- KR> Backfiring at idle/slow speeds Dan Heath
- KR> Backfiring at idle/slow speeds phillip matheson
- KR> Backfiring at idle/slow speeds Mark Langford
