Nawlens Gator
Member
I posted the last 2 days about a recurring hot coil issue on a '72 IH 140. It is 12 V neg ground with 10SI alternator and pertronix electronic ignition. Tractor runs great for 30 min to one hour then spits, sputters, and cuts off. It won't crank back up. I notice the coil is red hot when this happens and the ammeter shows a large current drain. I switch the key off and after things cool for around 30 min it cranks right back up, all seems normal, and things repeat.
I checked voltages at several points while running yesterday (not mowing) and everything seemed normal (alt 14.6 V to frame, coil neg terminal to frame 11.3 V) except the coil got too hot to hold a hand on after 60 min. Afterwards I swapped that ic14SB coil (3.4 ohm) for a used pertronix coil (3.1 ohm).
Today I installed a 1.6 OHM ceramic encased ballast resistor in the wire from the ignition switch to the + coil terminal.
This dropped the voltage to the coil from 11.5 V to 8.5 V (measuring from the + coil terminal to the frame). The current must be 3/1.6 = 1.9 amps.
The tractor started right up but I didn't run it very long. I'll try mowing with it later this week. The resistor got pretty hot pretty fast.
Hopefully this will help increase run time.
The plug wires are a solid core high performance set from Brillman. The tech reps from both Brillman and Pertronix said the plug wires were not an issue. The resistance on these wires I measured on the 1 foot wire from the coil to the distributor input was 0.5 Ohm.
The Pertronix tech rep also said their flame thrower coils (which I switched to) get hot, up to 200F, and can burn you if touched. This just didn't sound right (I haven't noticed this on my other 2 tractors) so I am trying the ballast resistor as recommended by several posters. The rep said if the tractor cranks up then the coil is still good. He suggested the hot coil is just a coincidence and something else is the issue. Since the tractor runs great after the coil cools off I'm not so sure I concur. I checked the fuel lines and both strainers and everything is clean.
Any thoughts on whether the lower coil voltage will damage the ignition module, plugs, etc.?
If this doesn't fix things I might try the Ignitor II coil and ignition module. They're pricey though.