Fuel Injected Flamethrower (Condensed)

[Luminaring]

Fun. I think you have bad valve surfaces, and a hot flame shoots up the intake manifold and out the throttle body injection to where the air filter would be.

[sgrannel]

No, I'm doing this on purpose. My gasoline controller has imperfections I never bothered to tune out. Lean transient backfiring is a well known effect that I can also reproduce on my laboratory engine when running on methane.