[AT] tractor electrical question

[John Hall]

points, plugs, cap, rotor and coil are all new. I verified with my 50 
year old parts book and it has the same part# for coil as what online 
parts at Case is showing. The new coil has 12V on the outside, but the 
bill had 6V. Box was sealed up, but it came from overseas, so a lot of 
variables there

Point gap was verified when I had the distributor off and plate out so I 
could make sure weights were free and springs not broken.

I had my voltage regulator with me yesterday. When I tried to check at 
coil with engine running rough, it showed OL for whatever reason. I've 
checked so much stuff lately that I'm not sure but I think I got 6 and 
12 volt readings depending on where the points were once I shut the 
engine off. I tried checking the voltage with engine running at the fuel 
solenoid for reference and it was floating all over the place from 4 to 
13.5V. This was observed with the engine hot and running rough. With 
engine not running it holds steady a little over 12.

Last night I also found that the wire to the coil and the wire to the R 
terminal on starter solenoid can read 6V (little less actually) while 
the wire going to the fuel solenoid in the carb was reading 12V.

John Hall



On 8/26/2021 6:35 PM, Howard Pletcher wrote:
> It's not unheard of, particularly since many of those parts now come 
> from overseas.  To me, swapping with another if you can find something 
> to swap with would be the easiest way to prove or eliminate that as a 
> possibility.
>
> Make sure your points setting is close to spec and they are clean as 
> that would affect the ignition.  Have you looked at your plugs, not 
> thinking that's the problem, but if they are fouled or badly gapped, 
> they could have an effect.  You also might run it until it heats up 
> and needs the 12V to see if it still shows 6V to the coil.  If not, 
> then it's somewhere else in the circuit.
>
> Many of the other things suggested have no connection with the 
> ignition circuit.
>
> On Thu, Aug 26, 2021 at 5:12 PM John Hall <jtchall at nc.rr.com 
> <mailto:jtchall at nc.rr.com>> wrote:
>
>     Howard, you are leaning toward new coil and old coil are both bad?
>
>     John Hall
>
>     On 8/26/2021 3:47 PM, Howard Pletcher wrote:
>>     No, what he is reporting is just what should be happening.  With
>>     the points open, no current is flowing through the primary
>>     circuit and there is 12V at the + side of the coil.  When he
>>     bumped the starter and closed the points, the current flowing
>>     through the resistor in the primary circuit results in a voltage
>>     drop so that there is now 6V on the coil as intended.
>>
>>     The wire from the starter to the coil does send 12V directly to
>>     the coil, but this is only engaged while the starter is cranking
>>     in order to produce a hotter spark for starting and is not
>>     connected to 12V  the rest of the time.
>>
>>     The fact the coil seems to require 12V to its terminal when hot
>>     points to an internal problem in the coil as discussed by Dell in
>>     the Yesterday's Tractors article.
>>
>>     Howard
>>
>>
>>
>>     On Thu, Aug 26, 2021 at 2:53 PM Carl Szabelski
>>     <c.s.szabelski at gmail.com <mailto:c.s.szabelski at gmail.com>> wrote:
>>
>>          By the way, I believe it’s not the coil and is related to
>>         the cranking motor. Especially since the voltage drops when
>>         you bump it like you said. Something in the motor may be
>>         partially shorted or corroded, causing a voltage drop to the
>>         coil. The coil should always see 12V whether or not there is
>>         a resistor, internal or external. The resistor is essentially
>>         after the coil winding and drops the voltage after the
>>         winding, not before it. If the engine is running fine when
>>         you directly connect 12V to the coil, the coil is working
>>         like it should and is good.
>>
>>         Carl
>>
>>
>>
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> -- 
> Howard
>
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