Cub won't start

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Fool on the Hill Farm
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Cub won't start

Postby Fool on the Hill Farm » Sun Aug 28, 2016 6:55 am

I've got a 48 Cub that had been running fine until recently - fired it up but forgot to open the fuel valve and she conked out. opened the valve and she fired up but died and then wouldn't fire. after leaving it a while I made several more attempts when the starter stopped working. replaced starter and ign. coil. cranks fine - fan spins, rotor spins, smell fuel at the exhaust pipe, but no ignition. would appreciate any help you could give me!

Eugene
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Re: Cub won't start

Postby Eugene » Sun Aug 28, 2016 7:46 am

Ignition points changed and gap set??

What have you done to test the ignition system?

Battery powered ignition system, magneto, or magneto converted to external coil?
I have an excuse. CRS.

staninlowerAL
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Re: Cub won't start

Postby staninlowerAL » Sun Aug 28, 2016 8:14 am

Eugene has you covered, got to know what you have before determining what to do. Each ignition system has some differences that must be adhered to for it to run. Stan

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Fool on the Hill Farm
Posts: 10
Joined: Sat Jun 25, 2016 9:55 am
Zip Code: 18930
Tractors Owned: 1948 Cub
Location: Durham Furnace, PA

Re: Cub won't start

Postby Fool on the Hill Farm » Sun Aug 28, 2016 8:15 am

Ignition points changed and gap set??

What have you done to test the ignition system?

Battery powered ignition system, magneto, or magneto converted to external coil?


it has a battery pwrd ignition - not sure about magneto/magneto converted to external coil? - there is an external ignition coil. haven't touched the points yet - just removed the cap to check the contacts and make sure the rotor rotated when cranked. I had checked by grounding a plug wire for spark which seemed weak so I figured I was in for a pound with the new starter might go in for a penny with a new coil. I need to check the ignition switch

Eugene
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Re: Cub won't start

Postby Eugene » Sun Aug 28, 2016 8:32 am

Fool on the Hill Farm wrote:I need to check the ignition switch
Since you have a weak spark from a plug wire - not the ignition switch.

Does the tractor still have a 6 volt battery?

Does the new coil have an internal resistor?

Block the ignition points open, piece of paper will do. Ignition on, check for battery voltage at the points.
I have an excuse. CRS.

staninlowerAL
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Tractors Owned: Cubs: (3)'49's, (1)'52, (1)'57 IH Cub LoBoy w/FH, (1)'72 154 Number Series Loboy, '76 Longstripe w/FH, Mowers: C-22, Bush Hog 412, Pennington 59, Woods RM42CF, Woods 42, assorted FCub plows, planters, discs, etc. OTHERS: '49 AC B & Ind. Sickle mower, '61 AC D12 Ser 2, '52 8N, '56 Ferguson 35 Deluxe, '53 MM BG (offset), (2) '49 Avery V's, '56 JD 420C, with Blade and fire plow, '85 JD 850 (Yanmar) w/72" belly mower, '76 Yanmar 1500, Sears Surburban's, MTD's, Jeeps & other misc. "treasures"
Circle of Safety: Y
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Re: Cub won't start

Postby staninlowerAL » Sun Aug 28, 2016 8:38 am

Does your ignition look like this with an external coil? The OEM IH J4 magneto coil is underneath the square cover and may or may not still be in place. If you file or replace the points, set the gap to .013.
magneto_plug wires1.jpg
If you have an external coil (as stated) with a magneto check to make sure there is a spark at the points each time the engine rotates. You can do this with a tester at the point where the wire from the coil connects to the post on the mag or observe the points opening and closing. A picture of your ignition system would clear up a lot of this. Stan

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Fool on the Hill Farm
Posts: 10
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Zip Code: 18930
Tractors Owned: 1948 Cub
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Re: Cub won't start

Postby Fool on the Hill Farm » Sun Aug 28, 2016 9:16 am

no - not like that - so I guess mine is a conversion then?
P8280002.JPG

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Fool on the Hill Farm
Posts: 10
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Zip Code: 18930
Tractors Owned: 1948 Cub
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Re: Cub won't start

Postby Fool on the Hill Farm » Sun Aug 28, 2016 9:19 am

and yes Eugene it's 6 volt and the new coil has an internal resisitor

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Glen
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Re: Cub won't start

Postby Glen » Mon Aug 29, 2016 9:52 pm

Hi,
If the 1948 Cub has Battery Ignition, someone probably converted it in the past.
The point gap is .020 inch for a Battery Ignition unit.
I don't know if you have any interest, but the coil was originally on top of the unit, under the hood, with a bracket to offset it some, so it fit with the generator bracket that the Cub has.
Here is a page from the Cub owner's manual showing how to replace the points. :)

http://farmallcub.com/rudi_cub/www.clea ... age-32.jpg
Attachments
Cub.jpg

Gary Dotson
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Re: Cub won't start

Postby Gary Dotson » Tue Aug 30, 2016 7:11 am

A 6 volt coil should not have an internal resister, your coil is for a 12 volt system.

staninlowerAL
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Posts: 3069
Joined: Fri Oct 29, 2010 11:34 pm
Zip Code: 36558
Tractors Owned: Cubs: (3)'49's, (1)'52, (1)'57 IH Cub LoBoy w/FH, (1)'72 154 Number Series Loboy, '76 Longstripe w/FH, Mowers: C-22, Bush Hog 412, Pennington 59, Woods RM42CF, Woods 42, assorted FCub plows, planters, discs, etc. OTHERS: '49 AC B & Ind. Sickle mower, '61 AC D12 Ser 2, '52 8N, '56 Ferguson 35 Deluxe, '53 MM BG (offset), (2) '49 Avery V's, '56 JD 420C, with Blade and fire plow, '85 JD 850 (Yanmar) w/72" belly mower, '76 Yanmar 1500, Sears Surburban's, MTD's, Jeeps & other misc. "treasures"
Circle of Safety: Y
Location: AL (Southwest)

Re: Cub won't start

Postby staninlowerAL » Tue Aug 30, 2016 7:30 am

Agree with Glen and, from your picture it looks like your mag ignition has been changed out for a battery/distributor ignition. Your description of the coil sounds like it may be the problem as Gary said. You can check the voltage at the distributor where the coil wire attaches or at least check for power at that point when the points are open. When the points are closed the power flows to ground and when opened again you should see a bright spark at the points. If this does not happen determine the cause. Stan

Eugene
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Re: Cub won't start

Postby Eugene » Tue Aug 30, 2016 8:10 am

Fool on the Hill Farm wrote:I had checked by grounding a plug wire for spark which seemed weak.
Faulty condenser will cause a weak spark. Could be a couple of other problems.

Conduct the previously mentioned voltage checks. It takes a minimum of 4.5 volts to adequately fire the coil. Could be a significant voltage drop caused by corrosion.

I would put the distributor on the bench, replace the points and condenser, inspect the rotor and distributor cap.

Glen has posted a link on how to replace points. Just be sure to set engine on #1 cylinder TDC before starting.

Remove the 12 volt coil and replace with your old 6 volt coil.
I have an excuse. CRS.

Jim Becker
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Re: Cub won't start

Postby Jim Becker » Tue Aug 30, 2016 12:11 pm

From the picture, it looks like your coil says "6V" right on it. Where did you get the "internal resistor" idea?

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Glen
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Re: Cub won't start

Postby Glen » Wed Sep 07, 2016 10:27 pm

Hi,
Here is a page from TM Tractor showing the offset coil mounting for the Cubs, if you don't have one, or want to buy one. There are pics below on the page showing where it goes.
You could check the gas cap vent holes too, they have to be open or the gas won't flow from the tank for much time. :)

http://www.tmtractor.com/new/el/947fp.htm


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