Posted by Nawlens Gator on March 24, 2015 at 11:13:32 from (184.46.86.83):
I posted yesterday about a problem with coils that seem to keep burning up on my '72 140. After 30 or 40 min the tractor just cuts off while mowing (normally at the furthest point from the barn) and the coil is red hot (even with a new coil). After sitting for about 20 or 30 minutes the coil cools off and it cranks back up and runs for awhile then repeats. This makes me suspect the coil but it may be coincidence. I have put new coils on 3 times chasing this problem and replaced the alternator to no avail. (
The alternator (2nd one, it's been on 6 mos)is a 10SI 12V neg ground and the coil is a ic14sb from NAPA. Tractor has an electronic ignition purchased from this site.
Today I cranked it up, set at mowing rpm's, and read voltages with a Fluke 177 multi-meter every 5 or 10 min. I measured voltage from Alt output to frame, and from coil output to frame. I also cupped my hand around the coil to get an idea of how hot it got.
The Alternator put out a steady 14.6 volts for 90 minutes. The coil (3.4 ohms cold resistance)output started at 10.1 volts when first cranked and cold. At 20 min the coil output had risen to 11.4 volts and had warmed but I could keep my hand on it.
The coil output stayed at 11.3 volts and it had warmed up at 40 min such that I could only cup it in the palm of my hand for 5 sec.
At 60 min I heard sputtering and the coil voltage was gyrating between 9.5 & 11.3 V. It smoothed out eventually and didn't repeat. Could the electronic ignition cause this?
At 80 min, coil voltage was 11.1, and I could only hold it for 3 sec.
I then mowed for 10 min and at 90 min coil voltage was 11.2 and I could barely hold it for 3 sec. I then shut down.
For some reason it didn't cut off like it normally does after 30 or 40 min.
The alternator and internal voltage regulator appear to be OK. I'm not sure about the coil and elec ignition. Is this coil output voltage normal. It seems the coil heated to over 140 deg F, but when it cuts while mowing it's much hotter. I need to change something, but just not sure what. Is there a better coil I can buy than ic14sb? Should I swap the elec ignition?
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