Loss of spark

T

Tractor Rod

Well-known member
Help……I was pretty pleased this evening after putting a new carb on my cub and it started right up. After running about three minutes it abruptly died. I of course checked that it was getting fuel and it was. Next I dug out my in line spark tester and it has list spark. Where would I start trouble shooting the electrical system before I start replacing the coil to find out what happened?

Thanks………

Rod
 
First thing I would check is do you have a spark as the points open and close (with the ignition switch in the run position)? JMHO Stan
 
Hi,
I guess the Cub has little spark, you wrote above it has list spark.
You didn't say the year of the Cub. In a post you made before, you said it is a 1948, I guess it has a magneto.
A spark tester that flashes doesn't show the power of the spark too well, unless it is different than I have seen.
I would test the power of the spark the magneto is making.
Be sure the Cub doesn't roll while doing the spark test.

Remove the ignition wire from the center post on the distributor cap, and hold the wire by the insulation, with the metal end about 1/4" from bare metal of the engine block.
Be sure the transmission is in neutral, turn the ignition switch to on, and run the starter.
The spark should jump the 1/4" gap, and be blue or white. A yellow spark is weak, and needs improving.
The engine may not run, or run right, with a yellow spark.
Do the test in a building, or not in bright light, so you can see the spark well.
The battery should be fully charged for the spark test. Charge the battery if necessary.
A low output charger is better, it may take several hours to charge it.
I sent you a PM.
 
You wrote it has list spark.
Click to expand...
I'm thinking lost spark.

No cost. I would grab the multi-meter and check for voltage, ignition on, at terminal on the side of distributor. Then check the condition of the points.
 
Thanks everyone.

GLEN, I’m sorry I should’ve mentioned it is a 1953. I actually have a 48, 51, and a 53 cub at this time. It has a distributor on it? Your thoughts knowing it’s not a magneto. I think I better break down and order a service manual. My electronic and ignition experience is very minimal!
 
Thanks for saying what year the Cub is.
Yes, a 1953 Cub probably has a Battery Ignition unit.
The spark test I wrote above is the same for a Battery Ignition unit.
Checking the points is a good place to start. They get burned from use, when they get burned enough, the engine won't run.
The Cub operator's manual has lots of info about things to service on a Cub.
The Cub service manual is made more for rebuilding the engine, clutch, transmission, etc.
There is a 1952 Cub operator's manual at the top of the page at Quick links, then go to PDF Manuals.
Below are pages showing the Battery Ignition unit. The 1st page shows what it looks like, if you need to identify it. The coil could have been replaced with the more modern style coil.
The 2nd page shows the points.
If the breaker cover is stuck in place, turn it left and right some to loosen it up. Don't pry much on it, it can break prying on it.
https://farmallcub.com/rudi_cub/www.cle ... age-11.jpg

https://farmallcub.com/rudi_cub/www.cle ... age-12.jpg

The points need the right gap to work right, .020"
The points can be removed and filed, or replaced.
I use a lawn chair, and sit down next to the engine. You need a good light, and I put a large towel on the floor to catch any small screws I might drop. Loosen the nut holding the end of the point spring, and it is usually made so the point will slide out.
Hold them one at a time with one hand, on something solid, like a vise. I use a large flat file. Wipe off all filings with a clean rag. Or you can replace the points.
If it has no spark after filing or replacing the points, the condenser or coil could have quit.
I sent you a PM, you get to it at the top of the page.
 
Tractor Rod":3ilqj5zz said:
Thanks everyone.

GLEN, I’m sorry I should’ve mentioned it is a 1953. I actually have a 48, 51, and a 53 cub at this time. It has a distributor on it? Your thoughts knowing it’s not a magneto. I think I better break down and order a service manual. My electronic and ignition experience is very minimal!
Click to expand...
Follow the above referenced links and download GSS 1012. It has complete service, maintenance and installation instructions for both the battery and magneto ignition systems as well as a lot of other relevant information. JMHO Stan :hattip:
 
Hello all,
I am at a total loss on my 1953 cub “no spark” issue. I have followed everyone’s advice and put on a new coil, put in new points and condenser. Still no spark to the plugs. I hope I don’t have to rewire the whole tractor……nothing is working. Any other ideas much appreciated!

Thanks,
Rod
 
Too bad it doesn't have spark.
I would check the voltage at the coil with a test voltmeter, if it is a Battery Ignition unit. See if there is battery voltage going from the ignition switch to the coil.
The ignition switch could have quit, or be corroded inside, so it only works in one spot. If you don't get a voltage reading at the coil, try working the switch many times from off to on, then test it again at the coil. You haven't looked at the PM I sent to you days ago.
 
staninlowerAL":1j1h2w89 said:
First thing I would check is do you have a spark as the points open and close (with the ignition switch in the run position)? JMHO Stan
Click to expand...
What was the result of this test? If you do not have a spark at the points as I described you will not have a spark at the plugs.
 
GLEN, thanks for your reply, and I’ll have to show my ignorance when it comes to this form. I looked at the two links you sent in the middle of one of your messages, but obviously can’t find the p.m. Thanks, Rod.
 
Look in the upper right corner of this page. You should find “Private Messages” with a red flashing number. Click on that number.
 
Hello all…. Just a quick follow up to let you know what happened. I replaced points, condenser, coil, plugs and checked the switch and all is working fine. I hope I have finally figured out the problem and I’ve ordered a new wiring harness. When I was checking the switch I noticed that when I put the positive Post on and off that it sparked. When I turned off the switch, it quit sparking. Therefore, I’m guessing that I have a short somewhere in the old wiring and hope that the new harness will fix the issue. When I ran my tests I had power to the positive side of the distributor.

Does this sound like maybe I’m on the right track?
 
with the switch on it would spark as you created a draw on the system which is ok switch off no spark is ok
 
So getting spark when the ignition switch is on with the load is normal, so what does everybody think at this point? Is my next step to replace the whole wiring harness per my last post? I hate to do the whole wiring harness routine, but don’t know what else to do? Thanks, Rod.
 
If the Cub has a Battery Ignition unit, the electrical system has to send battery power to the coil, so the engine will run.
You didn't say if you tested the battery power connection at the coil to see if it has battery power.
If it is a 6 volt system, it should have the same voltage as the battery has. Test the voltage at the battery first, and see what the battery has.
I haven't seen pics of it, but I don't think you need a new wiring harness, unless it looks bad.
You haven't said if it is 6 or 12 volts, positive or negative ground.
If there isn't battery voltage at the coil, try making a jumper wire from about number 12 wire, to go from the starter post, to the post on the coil that is connected to the ignition switch. Put a clip on each end of the wire. Be careful to not touch anything at the connections that would short the system.
Then see if the engine will run.
 
With switch on you got spark from battery post cause your points were closed and this has nothing to do with the wiring!!! --- check inside the dist, connections for short. The insulator where the wire goes in to the points sometimes gets cracked/worn/weathered and shorts out.-- not saying this is your problem but it can/has happened before.
 
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