That can be a trickey one. What often happens is that fuel is flowing into the pressure line from the cap (gravity overcomes exhaust pressure). That fuel acts as an obstruction and reduces fuel feed pressure to the carb. This leans 'er out enough to flame out. After the marshal flips the car over it can take a few seconds for the fuel to clear out of the pressure line. That's why you can still flame out after the car's been marshaled.

Another thing that can happen is that if you rev the engine too much when the car's upside down (or you're getting the 'slow marshaling' and it's on the lid too long) then you get a big air bubble in the fuel line because the pickup's uncovered (unless you have a Losi or HB truggy or buggy with a clunk tank). About the time that your car gets marshaled and you hit the gas, that air bubble hits the carb and you flame out...


What can help both situations is to do moderate 'blips' of the throttle while the car's on the lid. Don't rev the pee outa it, but don't let it just sit and idle. Moderate blips help keep enough pressure in the pressure line to slow the fuel flow into it without blasting lotsa air into the feed line. A clunk tank helps with the upside-down air bubble issue, but does nothing for the flooded pressure line issue. Refraining from mashing the trigger imediately after the car's marshaled helps let the fuel clear out of the pressure line. Roll the throttle on instead...