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Andyman is right..."advancing" the intake cam WILL reduce lobe separation angle, not widen it. You want to retard the intake and/or advance the exhaust to widen lobe separation, which is the net effect of increasing valve lash (ignoring the change in lift). That lawnmower probably didn't overspeed as most small engines are rev limited in the valve train, but probably started to warm up and the connecting rod and crank throw expanded faster than the block until you smacked the piston into the head. If the connecting rod was the weaker link, there she blows. You probably would have been fine if you kept the (probably about .040" thick) gasket but milled the deck by .010 or so.
garys_1k: you ignore the law of conservation of energy. Climbing a mountain uses more fuel per mile driven but that fuel isn't just pissed into the wind. The energy from burning it is converted into potential energy due to the change in elevation of the vehicle. As mechman600 stated, if he EOC's down the back side of the mountain he's burning ZERO lbs per mile and recovering the potential energy. Dragging a boat anchor to run at peak BSFC *is* pissing fuel into the wind because you've got nothing to show for it in the end. Climbing a mountain is different. BSFC is not and won't be a red herring as you use and/or tweak your BSFC (more accurately iso-efficiency islands) to determine if you are indeed better off running at high load at lower speed or lower load at higher speed. There's often overlap or times when the unintuitive is better.
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