Sun May 22, 2011 7:46 pm
I bought this rebuilt cub about a year ago and it has a rebuilt engine, new carb, plugs wires, condensor, points pretty much eveything is new and some twice. What it does after a while (20-30 minutes) it starts missing, progressively getting worse until it will eventually quits. The coil seemed to be getting hot so we replaced it off of a buddies parts tractor and still the same. The coil off the parts tractor looked new and stated it needs no external resistor. The coil still seems to be getting hotter than we think it should. Also a new thing we found was when it started missing we took a voltage reading at the battery when it starts missing and the voltage was cycling really high up and down really fast (saw readings as high as 68). The amp meter cycles back and forth also. We thought maybe the voltage was from the starter/generator/regultor so we completely unwired them while it was running and it was still there like the coil is back feeding. The negative side of the coil is wired to the distibutor. [url]:lost:[/url]
Sun May 22, 2011 9:09 pm
It does sound like the coil is getting too hot and failing. My guess is something is not wired correctly. It's not uncommon on a rebuild to have something wired backwards, and those kinds of problems are the worst kind to have. You basically have to get a wiring schematic and trace every wire. You might start with the starter/generator leads.
Sun May 22, 2011 9:17 pm
I thought that might be possible but we disconnected all the wires on the starter generator and regulator while it was running which completely isolated it and it was still missing and voltage was still cycling.
Mon May 23, 2011 5:52 am
If you were using a digital meter, repeat your test with an analog meter. Electrical noise from the charging and ignition systems will drive most digital meters crazy, causing the sort of readings you're getting. It might still be high charging voltage causing your problem.
Mon May 23, 2011 11:09 am
Did it ever run correctly?
When it quits, does it have a spark?
Are the old and new coils both 12 volt?
Does it quit with the parts tractor coil installed or does the coil just get hot.
Since the starter/generator is disconnected then I would not worry about over charging or even what the meter reads. Wrong coil, i.e. a 6 volt coil or a point gap too small can cause overheating of the coil. Also may have nothing to do with the coil or spark. When it dies check for spark.
Mon May 23, 2011 10:03 pm
When it runs it runs like new. Went to the parts store and got a 12 volt coil and an external resistor hooked it up witout the votage regulator and it ran for 2 hours without a problem. Im gonna get a new regulator then recheck voltages with a new meter. I think it might of been overcharging damaging the coils. It doesn't seem to have high cycling numbers with new coil and resistor at the battery.
Tue May 24, 2011 9:46 am
My new regulator will be in tomorrow so I guess my next question would be can the generator create too much voltage where the regulator can't knock it down? And what should the voltage readings be at the battery?
Wed May 25, 2011 6:59 am
Might not have anything to do with the regulator or the generator. Perhaps the voltage spikes were due to a faulty coil.
You mentioned that the spikes went away after changing the coil. Do you think that part of the coil was shorted to ground?
Another theory is that one of the spark plug wires was leaking current to ground. A voltmeter only measures differences and if the ground is noisy, then the reference point will be as well.
Start the tractor and spray the spark plug wires with soapy water in a windex bottle. If it is dark enough (inside a barn) then you will see where the wires are leaking current. Replace or rearrange the wires so they do not have a path to ground.
Wed Feb 19, 2014 8:51 pm
Did you ever find the problem. I have replaced Coil, distributer, carb, intake manifold, battery, plugs with plug wires, cleaned gas tank and replaced filter and gas online with the bowl, the battery and wires to it. Does just like yours. It came out of a barn and has benn sitting for a couple years. Ran good when parked.
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