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1948 Cub Mag Problems

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On2Wheels

07-16-2007 19:04:25




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Ok here I go. I have a 1948 Cub and I am trrying to get it back to stock - 6 Volt and with a Mag. I have bought a mag, installed it the way my I&T manual says and timed it. I just won't start. Someone told me there was a timing mark under the gear that drives the rotor so I tried adjusting that. At one time I did get it to run - very poorly. Can someone clue me in on the magic I need with a Mag.
Thanks.

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On2Wheels

07-20-2007 05:41:46




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 Re: 1948 Cub Mag Problems in reply to On2Wheels, 07-16-2007 19:04:25  
Are we all talking about the J4 mag that is (I think) Cub specfic?



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riowens1

07-18-2007 08:07:40




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 Re: 1948 Cub Mag Problems in reply to On2Wheels, 07-16-2007 19:04:25  
Had the same problem with my 48 Cub, the book tells you to have the engine"s #1 cylinder at TDC, and point the rotor in the mag at #1 plug tower, if you do this the engine is firing late, when the #1 piston reaches TDC, the mag should have already fired. Set the #1 piston on TDC, rotate the mag to #1 plug tower, and snap it, you may have to pull the govenor, and line it whith the groove in the mag, but I assure you it will run fine and you will have the ability to retard or advance the mag to get the timing exact but thats what you have to do.

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On2Wheels

07-19-2007 08:12:43




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 Re: 1948 Cub Mag Problems in reply to riowens1, 07-18-2007 08:07:40  
Where is the groove on the mag? Thanks.



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teddy52food

07-17-2007 06:02:00




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 Re: 1948 Cub Mag Problems in reply to On2Wheels, 07-16-2007 19:04:25  
Those gears have to be in time. There is a tooth on the small gear that is marked (beveled). The large gear is marked L & R. Time it on the R . L is for a diesel.



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On2Wheels

07-17-2007 06:04:03




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 Re: 1948 Cub Mag Problems in reply to teddy52food, 07-17-2007 06:02:00  
Do you mean the large gear - the actual rotor?



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teddy52food

07-17-2007 06:15:13




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 Re: 1948 Cub Mag Problems in reply to On2Wheels, 07-17-2007 06:04:03  
No. Take the rotor off & there are 2 screws holding a small plate. Under this plate is the large gear. You may have to clean the grease off the small gear to find the marked tooth. Put some grease in there again after you get it in time before you put the plate back on.



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On2Wheels

07-17-2007 07:43:06




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 Re: 1948 Cub Mag Problems in reply to teddy52food, 07-17-2007 06:15:13  
After I take the screws out of the rotor housing the next thing thing would comeoff is the larger plate (held on by 3 screws) where the points and condenser are. This is a J4 mag.



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El Toro

07-18-2007 07:51:10




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 Re: 1948 Cub Mag Problems in reply to On2Wheels, 07-17-2007 07:43:06  
Did you get the engine to run? Hal



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El Toro

07-17-2007 00:29:52




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 Re: 1948 Cub Mag Problems in reply to On2Wheels, 07-16-2007 19:04:25  
You need No1 piston at TDC on the compression stroke. Remove No1 sparkplug near the radiator and hold your thumb over the plug hole while someone slowly handcranks the engine. Once you feel the compression you can drop a large handle screwdriver into the plug hole and as someone
cranks the engine you watch the screwdriver rise
until it stops. Don't drop this into the cylinder.

Then take a look at the notch on the damper pulley to see if it's aligned with the pointer.
Pull the cap off the mag and see where the rotor is pointing. It should be at the No1 plug tower.
Your plug wires should be in this firing order:
2-1 The rotor turns CW.
4-3

If the rotor is off you will need to remove mag and rotate the rotor to the No1 plug tower and reinstall the mag. Hal

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On2Wheels

07-17-2007 03:42:37




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 Re: 1948 Cub Mag Problems in reply to El Toro, 07-17-2007 00:29:52  
That is exactly what I have done. When the mag "winds up" before it snaps where should the rotor be?



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El Toro

07-17-2007 04:14:03




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 Re: 1948 Cub Mag Problems in reply to On2Wheels, 07-17-2007 03:42:37  
I have never looked at the rotor when the impulse coupling snaps. Are you getting fire to the plugs? Pull off the coil wire from the cap and hold it near a good ground while someone makes an attempt to start the tractor. Should have a good
hot blue spark. I would remove the grounding wire
for the time being too. Did it run before installing the mag? Hal



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On2Wheels

07-17-2007 06:02:10




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 Re: 1948 Cub Mag Problems in reply to El Toro, 07-17-2007 04:14:03  
Yes it ran great. I checked the spark and it appears to be ok. When it did run I really ran poorly. I could tell it was a timing type sound to made. While running I pulled off each plug wire and it ran worse so that tells me it isn't missing.



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