[quote=DanH;1403378]Scott, consider the waste spark, arriving at the top of the exhaust stroke, or a little before. Both valves are open, thus it's not possible to generate significant cylinder pressure. Even if a combustible mixture is ignited, absent pressure there can be no kickback. Kickback has a single cause, ignition inside the closed cylinder too far before TDC?
Disagreeing with DanH is sure way to getting in trouble but I must disagree as well. The combustible mixture to be worried about is the residual fuel laying in your Sump. I?ve heard reputable stories of catastrophic events like blowing sumps apart while starting an engine with ponded fuel present. I had my own experience before installing a sniffle valve where the fuel/fumes ignited and caused a very loud boom/explosion and upon inspection I found the pressure from the explosion had pushed 2 of the orange silicone o rings off of their respective intake tubes and their shredded remains were laying in the bottom of the cowl. I think it?s foolish not to have some sort of intake drain on horizontal induction engines. I don?t think the factory would be using them if they didn?t think they were necessary. Just because you haven?t had an explosive event it doesn?t mean you can?t have one. The source of the ponded fuel is another discussion but I?ll just mention some injection systems leak/bypass fuel long after their shut down.