I've seen more than enough engines either lean or rich bog around a track for entire races without flaming. Then you see what appears to be a perfectly tuned car flame half way down a straight on the throttle. If that happens repeatedly in a day I would start looking for the problem. A engine doesn't have to be tuned PERFECT to stay running. Of course a tune way out of whack should be something to consider, but if you know your tune is close there's a problem.