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1948 farmall cub losing power when hot

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ludolph3
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1948 farmall cub losing power when hot

Postby ludolph3 » Mon Jun 02, 2014 6:03 am

Hello, have a 1948 Farmall Cub w/ magneto ignition. New plugs, points, condensor, plug wires. Starts good cold, runs bush hog w/ good power for 30-40 min. Then, starting out w/ pto engaged, sputters, misses and wants to stall. usually recovers and is ok until stopping and engaging clutch to mow again(max. load). If you turn the motor off or it stalls, will not restart - no hint of even trying to catch, just turns over. Next morning, starts fine when cold. Could it be the magneto winding? I would appreciate any advice, Thank you, Ludolph

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ludolph3
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1948 farmall cub losing power when hot

Postby ludolph3 » Mon Jun 02, 2014 6:31 am

I just posted a question about power loss on a 1948 Cub and forgot to mention it has a non-vented gas cap which could cause a problem. I have ordered the free vented cap. Thanks, Ludolph Conklin

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Barnyard
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Re: 1948 farmall cub losing power when hot

Postby Barnyard » Mon Jun 02, 2014 9:30 am

Sounds like it could be your coil. They will act like that when they get hot if they are going bad.
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Re: 1948 farmall cub losing power when hot

Postby Hengy » Mon Jun 02, 2014 10:05 am

You can check to see if it is fuel related by pulling the choke out slightly when it starts running rough. If it runs better with the choke, it is fuel related. If it still runs rough or rougher with the choke, you can eliminate the fuel system. To check the coil and points, when it starts running rough when hot or when it shuts off, immediately pull a plug wire and use an old plug to hold near a bare metal place on the engine. Spark when hot should still be nice, strong and blue. If it is weak or non existent, then it would be the coil breaking down.

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ludolph3
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Re: 1948 farmall cub losing power when hot

Postby ludolph3 » Mon Jun 02, 2014 11:42 am

Thanks, would that magneto winding they offer for sale on yesterday's tractors(around 70.00) do the trick?

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Re: 1948 farmall cub losing power when hot

Postby Hengy » Mon Jun 02, 2014 12:57 pm

So, this is still a Magneto-equipped tractor that has not been converted to run on an external coil? If so, then a "conditional yes" on your question. We'd need more information about how the tractor is set up.
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ludolph3
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Re: 1948 farmall cub losing power when hot

Postby ludolph3 » Mon Jun 02, 2014 4:28 pm

Yes, it has the original magneto system with the kill switch. I did replace the points, condenser and cap and it runs fine under load for 30-40 minutes. It absolutely will not start hot, not even a hint of a catch. I wasn't sure if the magneto "winding" was an internal "coil" which could go bad like an external coil can. It does appear to be the original magneto ignition, running off the engine. I don't see any signs of a conversion-no external coil. Thanks

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Re: 1948 farmall cub losing power when hot

Postby robertst » Tue Jun 03, 2014 9:35 am

I think Barnyards right on it being the coil,Good luck

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Re: 1948 farmall cub losing power when hot

Postby John *.?-!.* cub owner » Tue Jun 03, 2014 9:48 am

I am responding to this a little late, but have had the same problem with a magneto, and after fighting it for a couple months finally bit the bullet and bought another coil for it. Problem solved. I think the problem was my coil was a little weak, plus as an engine warms up the compression becomes a little higher. Higher compression requires a hotter spark to fire the plug, and it was crossing the line. I think there was a batch of coils made about 5 or 6 years ago that were borderline, and I had 2 of them . Which is lousy odds, since I have 4 magnetos. 3 on cubs plus 1 spare.
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