No spark 1949 Cub

K

kcsharp

Member
Hello:

I'm trying to get my grandpas 1949 cub up and going. We had it up and going enough to put a disc on and then one pass through the garden it died and won't start back up. I have checked and seem to be getting no spark at the plugs. I replaced the points and condenser (old points didn't look to bad) and still no luck. Yes there is gas in the tank and a good battery.

To get it running, (were originally not getting spark) we un screwed the wire that goes to the magneto to kill and and it started?
Read a lot about checking voltage at the coil but I'm not sure it has once of those like most of the post I search. It has the J4 magneto.

Looking for suggestions on how to trouble shoot what to start with. :lost: The points came with a 020 gap and looks like the owners manual says 013 so i will change that next time out.
 
Welcome to the forum. Go to Quick Links tab, top left corner of this page and search for GSS 1012 service manual for the J4 magneto. You will find a complete guide to maintenance, troubleshooting and repair as well as a detailed description of how the magneto works. Or bring it to a cubfest like Barnyard's Bash for expert help.
 
You should reset the points to 0;013" now, the 0.020" setting is way off. That affects timing as well, since the points effectively open sooner at the wrong setting. It also sounds like your kill switch is either grounding all the time, was in the wrong setting, or you have the wrong switch. A magneto switch is out to run, in to stop. If your switch has two wire terminals on the back side, it is the switch for battery ignition. Many owners have substituted that switch; they have to wire the second terminal to a ground, and then the switch must be used opposite the directions on it, that is, in to run, out to stop. The coil for a magneto is internal. Often they fail slowly, as they get hot, but sometimes they fail catastrophically, Lastly, when you replaced the points and condenser, you need to be sure the wire terminals aren't touching the case, and that the coil wire is still connected to the post as well. The insulators around that post are a common fail point also.
 
You also need to make sure that you got the gear on the rotor back in time when you put it back in. Even with the marks in line, you could have the rotor a half turn out of place.
 
Hi,
When you had the cover holding the rotor off the magneto, if you turned the engine, the timing could be wrong. You have to keep track of how you turn the engine when the cover is off.
The D shaped hole in the cover only fits 1 way on the shaft.
If the timing is wrong, you will need to find number 1 cylinder TDC, remove the cover, and turn the rotor so it is pointing to the number 1 post on the distributor cap.
That is if the spark plug wires are in the original positions on the cap.
Number 1 cylinder's wire is originally at the top of the cap.

When you test the spark, it should be blue or white, not yellow. Yellow is weak and needs improving.
It should jump a 1/4" gap.
Don't make the magneto produce sparks, without the sparks being able to jump to ground.
They have said on here it can damage the magneto coil to make sparks with no ignition wire connected, so the spark can jump to ground.

Below are pics from TM Tractor of the original Cub ignition switches, used in the 1940's and 1950's.

This switch is used with the magneto, it has 1 post.
It grounds the magneto to stop the engine, there is no battery power connected to it.
The 1 wire goes from the switch, to the post on the side of the magneto.

http://www.tmtractor.com/tm-tractor/gel ... ng_001.htm

This switch is used with the Battery Ignition unit, which came out in 1950 on Cubs. It has 2 posts.
1 post is connected to battery power.
The wire on the other post goes to the coil, which is mounted on a bracket at the Battery Ignition unit.

http://www.tmtractor.com/tm-tractor/gel ... ng_001.htm

TM Tractor at the bottom of the page has new ignition switches if you need one.
I have seen new, original style switches for the magneto for sale online.

They have said on here do not connect battery power to the post on the side of the magneto, it can damage the magneto.

The original magneto coil is under the cover on top of the magneto.
Sometimes if the original coil quits, people put on an automotive coil somewhere near the magneto.
Then they have to connect that coil to battery power.
You need to see which coil it has, to get the right ignition switch, and wire it right.

Below is a listing at TM Tractor for a new magneto coil, you can look at the pics.

http://www.tmtractor.com/new/el/713fp.htm

The insulation at the post in the side of the magneto can crack from age, then the power can short there.
I would check it.
Below is their listing for the insulation, it is where the end of the point spring is.
There is a magneto serial number shown in the listing that the part works for.
The magneto serial number begins with J4, I think.

http://www.tmtractor.com/new/el/957fp.htm

The rotor is gear driven. There are timing marks for the rotor and it's drive gear.
The timing marks should be aligned.
Below is a pic of the marks.
The area occasionally needs the old grease cleaned out, and new grease put on the gears too.
Check the gear teeth for wear.
TM Tractor has new parts for Cub magnetos. :)
 

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