Take the plug out and ground it to the cylinder.

Put a wood dowel or plastic stick down the spark plug hole untill it touches the piston.

Stand in front of the engine.

Turn the ignition ON.

Turn the prop counter-clockwise----------slowly.

Watch the wood dowel move up as the piston comes up in the cylinder.

Watch for the plug to spark.

Now, tell us when it sparked.
Was the piston all the way at the top of the stroke?
Or did it spark 28* BEFORE the top?
Or did the piston come all the way over the top and spark on the way back down?


If your plug really is popping when the piston is on the way down--then your magnet is in the wrong spot and it's tripping the ignition sensor at the wrong time.

Did you take the prop hub off? Did you put it back on in the right spot? Timing sensor can't really move that much. Almost impossible to screw that little bracket up.

Edited for clarity