stalls out when warm
Since the carbs have been all cleaned out w/ new jets and nice clean air filters, + the fact she goes fast enough to shift her into 4 gear. . .
It CAN be a bad coil. Having worked on the larger size gas engines for roto tillers and generators , I have found that a magneto coil can go bad- sort of. At an idle and about halfway up, the engine ran fine. The carb was brand new so I put in a new magneto coil in and the engine worked as it should.
Sometimes with a weak coil, the insulation is not what it should be and voltage jumps around. A hi voltage magneto coil is not much different than a battery ignition coil, both have a primary and secondary winding. The magneto coil is mounted or wound on a laminated iron core that allows a flywheel magnet to pass over or under it to make the current for the primary which gets opened an closed through points with a condenser across the points to absorb the back voltage when the points open.
ignition coils are very similar to a magneto coil, having a laminated core or a core of heavy iron wires and has both ends of the low voltage or
primary winding available. Bat+ goes into one side of the coil, other side of coil goes to the 'points an condenser' and of course bat- is grounded. Sometimes if both sides of a magneto coil's primary is available, I have wired the magneto coil up like an ignition coil because flywheel magnets were weak and the engine ran great. SO yes it can be a bad ignition coil at higher engine speeds. If one does not know a coil can go bad, ( because the engine does run ) the engine when run at higher speeds will start to **** out as if from lack of fuel, when in fact it is starving for a spark.