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At the risk of stirring up a hornet's nest of conflicting opinions: Pull the prop through forward or backward to clear a flooded engine?
My Continental engine operators handbook says: "...would indicate overpriming or flooding. This is remedied by turning ignition switch "OFF", setting throttle full open and pulling the propeller through three or four revolutions." [No mention in which direction.]
My Continental maintenance and overhaul manual says: "If the engine is over-primed, turn the ignition switch off, open the throttle, and turn the engine backward to unload the cylinders."
My Taylorcraft owners manual says: "If the engine loads up, put the switch in the OFF position, open the throttle wide and turn the prop backwards a few times to clear the engine."
But my Taylorcraft service manual says: "If the engine does not start immediately it may have too much fuel in the induction system. The switch is turned off, the throttle opened all the way and the prop pulled through several times in the normal direction of rotation. It is a common misconception that to rotate the prop backwards clears the engine. There is no basis for this thinking."
And every old-timer on the ramp at a fly-in breakfast where I flood my engine says "backwards."
So which is it, forward or backward?
On the old hand-propping thread here, someone mentioned that pulling the prop backward doesn't suck more fuel in, and would make only a weak spark if the mags were hot for some reason.
I can understand the safety rationale of turning the prop backwards, in case the ignition switch was left on or the mags weren't grounded.
But can somebody explain the mechanical justification for one direction or the other? Are you trying to push excess fuel back out the intake valves? Or push fuel vapor out the exhaust valves? What exactly do you accomplish within the cylinders by pulling the prop through (either direction) with the throttle open?
My Continental engine operators handbook says: "...would indicate overpriming or flooding. This is remedied by turning ignition switch "OFF", setting throttle full open and pulling the propeller through three or four revolutions." [No mention in which direction.]
My Continental maintenance and overhaul manual says: "If the engine is over-primed, turn the ignition switch off, open the throttle, and turn the engine backward to unload the cylinders."
My Taylorcraft owners manual says: "If the engine loads up, put the switch in the OFF position, open the throttle wide and turn the prop backwards a few times to clear the engine."
But my Taylorcraft service manual says: "If the engine does not start immediately it may have too much fuel in the induction system. The switch is turned off, the throttle opened all the way and the prop pulled through several times in the normal direction of rotation. It is a common misconception that to rotate the prop backwards clears the engine. There is no basis for this thinking."
And every old-timer on the ramp at a fly-in breakfast where I flood my engine says "backwards."
So which is it, forward or backward?
On the old hand-propping thread here, someone mentioned that pulling the prop backward doesn't suck more fuel in, and would make only a weak spark if the mags were hot for some reason.
I can understand the safety rationale of turning the prop backwards, in case the ignition switch was left on or the mags weren't grounded.
But can somebody explain the mechanical justification for one direction or the other? Are you trying to push excess fuel back out the intake valves? Or push fuel vapor out the exhaust valves? What exactly do you accomplish within the cylinders by pulling the prop through (either direction) with the throttle open?
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