This same thing used to be a big problem with Air-Cooled Porsche 911's with the Continuous Injection System (CIS) Because the cars were programmed lean for emissions purposes, they were already predisposed towards Lean Backfires through the airbox. Add in starting on a cold day, where the A/F goes even leaner, and they'd have a big problem with lean back-fires blowing out the airbox. They (Porsche) eventually installed a pop-off valve into the airbox to act as pressure relief, rather than correctly re-program the CIS to add in more fuel.
