12V Jump to 6V Not Running

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RSViewMan
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12V Jump to 6V Not Running

Postby RSViewMan » Tue Jul 09, 2019 6:05 pm

I have a '61 Cub (appears all original 6V) that the previous owner ran for an unknown amount of time on 12V. I placed a good 6V battery in it and now it will crank but not start. It runs like a champ on 12V -- will turn but not start on 6V. I verified the coil is 6V. I was thinking checking the points and re-gapping tomorrow. I am brand new to the Cub following and am hooked. Anybody have any other ideas? Thanks in advance for any help!!!

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radioguy41
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Re: 12V Jump to 6V Not Running

Postby radioguy41 » Tue Jul 09, 2019 6:19 pm

If it runs like a champ on 12v I would not mess with the points. How did you verify the coil is 6v ? Is there an external resistor on the coil ? If there is a resistor on the coil to drop it from 12v to 6v then with a 6v battery that resistor will essentially kill the voltage to the coil.
Last edited by radioguy41 on Tue Jul 09, 2019 6:27 pm, edited 2 times in total.
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Re: 12V Jump to 6V Not Running

Postby inairam » Tue Jul 09, 2019 6:22 pm

If the PO used a 12v Negative ground and you hooked up a 6 volt positive ground the wires on the coil could be reversed. + should be connected to the distributor and - to the ignition switch http://www.farmallcub.com/phpBB2/viewtopic.php?t=67284

Check for spark at the coil to distributor wire. The coil could be burned out.

If the wires are correct for 6 v positive ground and you have spark at the coil spray some starter fluid into the carb. If it almost starts on the next crank it is probably a fuel issue. If there is no change it is probably an ignition issue.

How did the PO charge the battery?
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RSViewMan
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Re: 12V Jump to 6V Not Running

Postby RSViewMan » Tue Jul 09, 2019 6:29 pm

radioguy41 wrote:If it runs like a champ on 12v I would not mess with the points. How did you verify the coil is 6v ? Is there an external resistor on the coil ? If there is a resistor on the coil to drop it from 12v to 6v then with a 6v battery that resistor will essentially kill the voltage to the coil.

There is a 6V label on the coil. There is not any resistor attached to the coil.

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Re: 12V Jump to 6V Not Running

Postby RSViewMan » Tue Jul 09, 2019 6:33 pm

inairam wrote:If the PO used a 12v Negative ground and you hooked up a 6 volt positive ground the wires on the coil could be reversed. + should be connected to the distributor and - to the ignition switch viewtopic.php?t=67284

Check for spark at the coil to distributor wire. The coil could be burned out.

If the wires are correct for 6 v positive ground and you have spark at the coil spray some starter fluid into the carb. If it almost starts on the next crank it is probably a fuel issue. If there is no change it is probably an ignition issue.

How did the PO charge the battery?


It ran as a 12V positive ground connection for some time by the PO -- too lazy/cheap to buy a 6V Battery maybe. I assume the PO charged the battery with an external charger (not with the generator).

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Glen
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Re: 12V Jump to 6V Not Running

Postby Glen » Tue Jul 09, 2019 6:37 pm

Hi,
Below is the 1955 Cub owner's manual. The experts on here recommend reading it, it has lots of info about operation, maintenance, and lubrication. There is a table of contents on page 1.
It has pics of how the Cub was originally. It has more info than the 1959 Cub owner's manual, which is in the list of manuals on here.

http://farmallcub.com/rudi_cub/www.clea ... index.html

Since you have just bought the Cub, it is a good idea to check the points, and point gap. If they are burned, it can make it start poorly.
There is a pic of the points on page 41 in the manual.

Dirty spark plugs can make it start poorly also, or spark plugs with the wrong gap.

Always a good idea to give a Cub you just bought a tune up, check the timing with a timing light, check or change all the oils, and the coolant in the radiator. The owner's manual shows how to service those things and more. :)

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Re: 12V Jump to 6V Not Running

Postby Eugene » Tue Jul 09, 2019 6:44 pm

Throwing in another thought. -- 6 volt starter needs to be rebuilt.
I have an excuse. CRS.

RSViewMan
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Re: 12V Jump to 6V Not Running

Postby RSViewMan » Tue Jul 09, 2019 6:47 pm

Eugene wrote:Throwing in another thought. -- 6 volt starter needs to be rebuilt.


Seems to crank strong - maybe not fast enough?

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Re: 12V Jump to 6V Not Running

Postby RSViewMan » Tue Jul 09, 2019 6:48 pm

Thanks for all of the suggestions. Will try to look at it tomorrow and post back.

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Re: 12V Jump to 6V Not Running

Postby Rick Spivey » Tue Jul 09, 2019 8:50 pm

Based on description this is not likely, but it doesn't have a solid state electronic ignition unit in place of points, does it?
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Re: 12V Jump to 6V Not Running

Postby Eugene » Tue Jul 09, 2019 9:42 pm

RSViewMan wrote:
Eugene wrote:Throwing in another thought. -- 6 volt starter needs to be rebuilt.
Seems to crank strong - maybe not fast enough?
If everything is in tune, the engine does not have to crank very fast. Hand cranking is very slow, but will start a Cub.

12 volts will crank the engine much faster than on 6 volts and require approximately 1/2 the amperage.

As others suggested, consider a complete engine tune up, including compression tests. If that fails check the starter condition.
I have an excuse. CRS.

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Re: 12V Jump to 6V Not Running

Postby RSViewMan » Tue Jul 09, 2019 9:59 pm

Rick Spivey wrote:Based on description this is not likely, but it doesn't have a solid state electronic ignition unit in place of points, does it?


Rick - it does not.

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Re: 12V Jump to 6V Not Running

Postby Scrivet » Tue Jul 09, 2019 10:07 pm

Wow! I haven't seen a shotgun pattern of possibilities like this in a long time. Seems like we're throwing a lot of "might be" at it without much diagnostics.

When was the last time it was ran on 12V? Did you try it again on 12V after putting the 6V battery in and it not starting? Have you checked the voltage at the battery and starter switch end of cable while starter is cranking? Where physically is the battery grounded (battery box, transmission cover bolt, or...)?

It's a new to you Cub and you're new to Cubs, did you pull the kill switch out when you tried to start it on 6V? Turn the gas on? (Both have happened to us all; more than we care to admit for a few of us)

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Re: 12V Jump to 6V Not Running

Postby RSViewMan » Wed Jul 10, 2019 8:51 pm

Scrivet wrote:Wow! I haven't seen a shotgun pattern of possibilities like this in a long time. Seems like we're throwing a lot of "might be" at it without much diagnostics.

When was the last time it was ran on 12V? Did you try it again on 12V after putting the 6V battery in and it not starting? Have you checked the voltage at the battery and starter switch end of cable while starter is cranking? Where physically is the battery grounded (battery box, transmission cover bolt, or...)?

It's a new to you Cub and you're new to Cubs, did you pull the kill switch out when you tried to start it on 6V? Turn the gas on? (Both have happened to us all; more than we care to admit for a few of us)


Scrivet - Thanks for all of the pointers and tips. Problem is solved. Replaced the coil and good to go. This site provides so much information -- even a newbie like me was able to troubleshoot it and find the issue with the coil. Thanks to everyone for the help!!!


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