Engine bogging down after 30 minutes

Guys, here's a bit more on what happens under the fan shroud..
those wires going to the ingnition modules are VERY sensitive to corrosion and moisture..
the magneto connection that energizes the HighVoltage is very low power..
WHen corrosion builds on the connections and dirt builds up around the assembly,
ANY moisture at all can cause a short-circuit across the magneto..
That reduces the power available to the spark, making the HV magneto coil "act" like it is bad.
..especially when it's cold outside, and the humidity is up.
But..
since this extra load against the coil is stressing the windings.. the coil overheats, damaging the coil,
and even though you may not have had the lost power when cold and wet..
you get the example of the day.. the opposite symptom.. it craps-out when it gets hot.
This is the actual bad coil.
Here's my point:
If you get the cold-weather symptom, most techs will replace the coils at your expense, and to their profit,
when usually, it's just the connections that need to be cleaned.

So.. EVERY time you have an excuse to take the fan-shroud off the motor,
clean the connections !!!
..and "heat-shrink" is your friend.

On off-road race cars..
we use a tiny dab of grease on the connections before we install the heat-shrink,
and it is "serviceably sealed" from moisture. ..aka.. Reliable.
 
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