Magneto coil question

Farmall Cub Forum -- Questions and answers to all of your Cub related issues.

Moderator: Team Cub

Forum rules
Notice: For sale and wanted posts are not allowed in this forum. Please use our free classifieds or one of our site sponsors for your tractor and parts needs.
User avatar
clodhopper
5+ Years
5+ Years
Posts: 793
Joined: Sat May 07, 2011 8:20 pm
Zip Code: 27526
Tractors Owned: 1950 Cub Demo
1978 Cub Cadet 1650
cub 193 plow
cub 174 planter
cub sidedresser
cub 144 cultivator
cadet 50C deck
Circle of Safety: Y

Magneto coil question

Postby clodhopper » Sun Mar 29, 2015 9:48 pm

Just refurbished a used J4 I picked up on the cheap. I had planned on replacing the coil assuming it was toast. After reassembly, I figured I would bench test it with the coil that came in it. Imagine my surprise when it lit up the test spark plug. It is however, an orange spark, and almost nonexistent at low RPM. Even at 1200 RPM it is orange, although a great deal stronger. Should't i be getting a BLUE spark? I suspect the coil is weak. What do you guys think?
Brad

User avatar
Super A
10+ Years
10+ Years
Posts: 4339
Joined: Mon Jan 26, 2004 10:53 am
Zip Code: 28521
Tractors Owned: 1949 Cub "The Paperweight"
Cub powered IH 52R combine
Grandfather's 1948 Super A
White demo Super A-"Ol Whitey"
1950 Super A "Old Ugly"
1954 Super A-1
856
Buncha other junk
Circle of Safety: Y
Location: NC, Jacksonville area

Re: Magneto coil question

Postby Super A » Sun Mar 29, 2015 10:37 pm

Replace the coil. A man that knows mags told me it should throw a blue spark across at least a 1/4" gap.

Al
White Demo Super A Restoration Updates

Let us pray for farmers and all who prepare the soil for planting, that the seeds they sow may lead to a bountiful harvest.

User avatar
John *.?-!.* cub owner
Team Cub Guide
Team Cub Guide
Posts: 22234
Joined: Sun Feb 02, 2003 2:09 pm
Zip Code: 63664
Tractors Owned: 47, 48, 49 cub plus Wagner loader & other attachments. 41 Farmall H.
Location: Mo, Potosi

Re: Magneto coil question

Postby John *.?-!.* cub owner » Mon Mar 30, 2015 8:56 am

As Super A said, the coil is probably weak. A cub magneto runs at half the rpm of the engine, so it's maximum rpm is 900. If it is weak at 1200, it is not going to start, even with the impulse tripping. The big test is at hand cranking speed with the impulse tripping on every cylinder. It should give a minimum of 1/4" spark then, with a really good one going 3/8". Normally the spark looks blue when hot, but a slight change in the surrounding gasses (air) will change that.
If you are not part of the solution,
you are part of the problem!!!

User avatar
Bigdog
Cub Pro
Cub Pro
Posts: 24142
Joined: Sun Feb 02, 2003 12:50 pm
Zip Code: 43113
Circle of Safety: Y
Location: OH, Circleville

Re: Magneto coil question

Postby Bigdog » Mon Mar 30, 2015 10:57 am

The coil is weak and they only get worse as they heat up. Time to replace it.
Bigdog
If you can't fix it with a hammer, you've got an electrical problem.

My wife says I don't listen to her. - - - - - - - - Or something like that!

Image

http://www.cubtug.com

User avatar
clodhopper
5+ Years
5+ Years
Posts: 793
Joined: Sat May 07, 2011 8:20 pm
Zip Code: 27526
Tractors Owned: 1950 Cub Demo
1978 Cub Cadet 1650
cub 193 plow
cub 174 planter
cub sidedresser
cub 144 cultivator
cadet 50C deck
Circle of Safety: Y

Re: Magneto coil question

Postby clodhopper » Mon Mar 30, 2015 11:37 am

Just as I suspected. Thanks for the input guys. :)


  • Similar Topics
    Replies
    Views
    Last post

Return to “Farmall Cub”

Who is online

Users browsing this forum: MiCarl and 10 guests