Is the Mixture broken?

[Viper2000]

I certainly agree that something is wrong with all the fighters (even the fuel injected German ones); but it's not obvious exactly what is causing the backfires. Mixture problems are implied by the flame colour, but the fact that the Moth doesn't suffer implies that the supercharger may be to blame, since that's the one difference between the Gypsy III/Gypsy Major and the afflicted engines.