I can't believe the comment above saying 2 strokes won't detonate, they do it quite readily. Who ever thinks that has had little or no experience with our 2 stroke engines. To much nitro, to high a compresion, flooding, to lean a setting--all can and will cause backfires to occur. The most common cause it setting the mixture to lean. Using to hot a plug might also contribute to backfires, especially if you are using high nitro content fuel or have a high compression head. Once an engine is properly set up, it is easy to start it by flipping the prop backward very hard, the resultant backfire reverses the direction and the engine will often run up nicely.