When you say Flywheel key is ok , did you actually remove the flywheel and look ? This is the last mistake I made on a Techumseh , It looked good from the top, new plug, new coil, lots of sanding and cleaning to end up with a sheared key.Do these things fail all at once or gradually? All relevant surfaces were buffed clean, tried different plug, tried different (used) coil. flywheel key is OK.
Chipper was unused for3 yrs +/-
Weak spark is not the problem. If a visible spark, no matter the appearance , you have spark. The appearance is merely an effect of the air in vicinity of the spark. the killovolts necessary to jump the gap are either enough to jump the gap or not enough and no spark.Changed the gap to .008 from .013 to no effect. The fire is barely visible jumping the gap on a spark plug. Gotta be something else.