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Ed- Gasses out the oil filler tube are blow-by causing by escaping exploded gas going through your rings into the engine block/pan. Since gas is "pumped" into the engine it has to relieve itself and escapes thru tube. It won't normally be there when engine is cold simply because oil hasn't fully pumped up into the rings, part of which is then gassified itself in the blow-by process. As oil finds its way to rings, as engine gets hotter, and as more blow-by pressure (including the exploded gas) builds in the block, then it starts to come out. Blow-by is not a pre-ignition by product. Pre-ignition can manifest as BACK fire thru carb (if timing is that far off or if intake valves are leaking enough) and as dieseling after shutoff (gas is still exploding due to residual heat in the cylinder). "Bad" gas and poor spark cause gas to explode rather than fizz-burn for a smoother, more efficient combustion. Bad gas or low grade gas has fewer hydrocarbons and burns hotter. This adds more heat to the cylinder. Don't think the sputter you hear intermitantly is pre-ignition, but MISS fire where the gas isn't being ignited at all. Poor compression, poor spark (tune-up stuff), bad plug wires AND arcing plug wires (in pitch black you can sometimes see very eerry looking electricity dancing across your wires), and other factors. Not a real problem on these low RPM, low compession engines unless it's running that way all the time. Then you have poor performance and you're wearing out the engine. Blow-by itself is not a problem, but keep an eye on oil levels.
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