Ernie Willson wrote:
First try the sparkplug gap trick. When voltage is low the spark cannot
make the large jump. Decreasing the jump can get a small spark through.
Usually, any spark that can jump the gap (when installed in the
cylinder) will run an engine, although it will not run well at low loads.

I assure you that if you pull the flywheel/magneto off you will
immediately see the condenser and the points. You cannot really check
the condenser. Check out the points for being properly adjusted
(gapped), and pitting. If this were my machine, since I'd gone through
all the work of getting the flywheel off I'd replace the condenser and
points regardless of apparent condition.

I'D ALSO REPLACE THE FLYWHEEL KEY SINCE THIS HAS CAUSED SIMILAR PROBLEMS
FOR ME IN THE PAST. If the key is partly sheared then the spark timing
can get messed up. The key can partially shear (without completely
breaking) if the blade stops very abruptly, like when hitting large
rocks etc.

HTH



Happens in conventional mowers, but is unlikely in a tractor as the
blade is not directly driven. If you replace it, do use a proper
aluminum key, a steel key defeats the purpose.