There were a few time ant heat related problems with the N. And contrary to popular belief.. vapor lock was never a big issue, on their gravity feed system.. as long as you left the fuel line in its oem position.. and without an EXTRA inline filter.
Here are some of the more common problems:
Marginal ignition switch. The switches were pretty substandard.. even by 1940's standards... they would slowly fail due to bad contacts making restive connections.. which get hot and then finally don't conduct enough to get power to the coil.. cooling helped.
Front mount ignition coil, and
ballast resistor. The ignition coil wasn't really a 6v coil.. even though the sytem was setup for 6 volts. It was more of a 3.5 volt coil.. And it used a ballast resistor with thermal properties to limit current and drop voltage to the coil. When you first started the tractor, the ballast resistor was cold, and at its lowest resistance.. it allowed higher than normal voltage to the ignition coil..say in the 4+ v range. This helped with starting. In a very short time, the ballast resistor cam up to temperature, and as it did.. its resistance increased.. dropping coil voltage down to about 3 ( min 2.5 max 3.5 ).
Thie ignition coil also was not very robust, and was prone to heat failures. The heat would melt the tar-like insulative materials and short some of the windings out, reducing spark output. ( on some coils, this became a cascade problem.. more heat+ more shorted turns+more heat+more shorted turns.. which eventually stalled the engine.. After cooling a couple hourse, the turns 'un'shorted and the tractor started... made it difficult for many a shade tree mechanic to troubleshoot. The most common cause for this failure was because someone bypassed the ballast resistor. Bypassing the ballast resistor put full battery power on the coil.. providing very good hot sparks. Unfortunately.. it only takes about an hour of this to start 'cooking' the coil'.
What would have been a better idea, instead of bypassing the resistor to up sparks, would be to have done a tune up... New cap, rotor, condensor, points, and plugs and wires. For the plug wires.. use a copper core wire.. like a hotrod shop may provide.. not a modern supressor wire. The N coil output was in the low KV by our ignition standards these days. 20kv or less.. The modern supressor wires and supressor plugs further reduce this.
Stock plug was a champion H-10 or AL 216.. Many now use a champion H-12 or a AL-437, a hotter range. helps with the no-lead gas
What some people have done, is to install a bypass switch on the ballast resistor.. and hit the switch when starting to help with a slightly worn out system. There are lots of ways to implement this from.. a manual switch.. a relay tied to the starter button, or even an oil pressure sending unit used as a switch.
In short.. it it is unable to start when hot.. If you are sure it is not a fuel delivery problem... then look at the electrical system.. Measure the votlage at the top of the coil.. with key on, and points open.. should be battery volts.. with key on and points closed.. should be 3.5. If it isn't.. try jumpering the key switch.
Fuel delivery can be checked by pulling th drain plug at the bottom of the carb. It should pee a good pencil sized stream an not taper off.
Soundguy
