Tue Apr 16, 2013 9:10 pm
Sounds to me like it is a coil issue as well. While you are in there suggest you may want to replace the rotor if there is a lot of slop. The problem you describe has had me befuddled for a long time till I finally figured out with Cecil's help a few years ago that it was a coil issue. If the coil is as I am assuming the internal one, then you can get pretty good coils from Mainely Magnetos, AI and others - even on
. The key is the core - you need that puppy to put the new coil on. The coil is a tad pricey, but for my money, fixing the mag properly with a proper internal coil is the ticket.Magneto Coil
Prices will vary from $60.00 to $75.00. Like I said, not cheap but well worth the investment IMHO. This is the search string - Farmall Cub Magneto Coil
Tue Apr 16, 2013 10:41 pm
Thank you all for the replies. I remember reading about these coil issues in another post as well. I am not sure if this matters, but what is the life span on a coil? I put a new coil, condensor, points in the magneto when I got the Cub about two years ago. While the tractor has done more sitting around then I would like I just kind of assumed that the coil was fine, but you know what that say about assuming. Also the coil that I put in it was from Steiner, are there different quaility coils and I simply did not buy a better quality one? Thank you all again, with the help on this forum I feel that I will be able to pin point this issue.
Wed Apr 17, 2013 5:09 am
Coil lifespan is a tricky question. I have 3 rebuilt mags, the oldest going on 6 years. However, I have heard of some coils only lasting 1 -2 years. Not accusing you of this, but if you ever snap the mag over without somewhere for the spark to go, you will shorten the life of that coil significantly. Check across the coil with an ohm meter, from primary wire to coil cab nub, and from nub to the ground strap under the clamp screw. It should read around 9500 - 10500 ohms. If no reading , or erratic reading, coil is likely dead. A good reading is NOT a guarantee of a good coil, but I would be less inclined to buy a new one at that point. Did you try my two checks from the earlier post, that could help point the way also?
Wed Apr 17, 2013 5:34 am
Had the same problem once....it was the coil....Just my 2 cents...Your getting some great advice, I'm sure you'll get it....Dave
Wed Apr 17, 2013 11:20 am
Thank you once again for the replies, I have classes most days this week, but when I find some time the first thing I am going to do is the run the tests that have been mentioned. Also I must admit I have snapped the magneto over a few times while not on the tractor or having any type of spark plug in it. I now know that is a big not to do. I did how ever snap the magneto over a few times with the spark plugs in it and noticed the spark was really not all that white/blue. It gave off more of a yellow-ish color. Can this also be a sign that the coil is going bad?
Thanks again guys, A.J.
Wed Apr 17, 2013 11:38 am
DelValCub wrote:It gave off more of a yellow-ish color. Can this also be a sign that the coil is going bad?
Yes, coil and or condenser.
Strip magneto down to where points are visible. Vise gently holding magneto with coil wire and spark plug grounded to vise. Snap over impulse coupling watching for an arc at the points. Yellow arc at points usually indicates a faulty condenser.
Wed Apr 17, 2013 11:39 am
Wed Apr 17, 2013 1:39 pm
I agree with Rudi, Make sure the kill switch is not 'leaking to ground'. bypass it. disconnect it.
Wed Apr 17, 2013 2:24 pm
Looks like I am on my way to finding the issue. I am a little unsure of what you mean Eugene when you say to ground the spark plug wire and coil wire to the vise. I know what you mean by grounding the spark plug wire, but should I disconnect the coil wire as well? Just making sure I do not cause more damage then I already have. Also one of the first things I did was dissconect the kill switch, so if there is one thing that I have eliminated the kill switch is it.
Wed Apr 17, 2013 3:27 pm
I had an issue similar to yours and what ended up being the problem was the insulator on the kill switch post....it had a hairline crack in the plastic insulator .....would run sometimes.....then wouldn't be able to start it again for days...it was especially bad when we had high humidity or rain.....which is how I finally figured out that it was the problem. .....
item 45 in this capture that I stole from Rudi's post.
Replaced it as had no issues since...
You do not have the required permissions to view the files attached to this post.
Wed Apr 17, 2013 3:43 pm
DelValCub wrote:I am a little unsure of what you mean Eugene when you say to ground the spark plug wire and coil wire to the vise.
Insert spark plug into coil wire. Lay spark plug on vise. Metal vise this will provide a circuit from the spark plug back to the magneto.
Thu Apr 18, 2013 4:57 pm
Well I did not have time to run the test on the magneto, but I attempted to start the Cub and it fired right up and ran for about 5 seconds then died and would not restart. The carb did seem to flood out too. While I am still going to run the tests on the coil and mag, the fact that it fired right up after sitting for 2 days ran for 5 sec and died would make me think it was a carb issue. Just figured I would add this info in the mix of issues.
Thu Apr 18, 2013 5:18 pm
DelValCub wrote:the Cub and it fired right up and ran for about 5 seconds then died. The carb did seem to flood out too.
Other way around. Ignition issue first.
Fuel issue - normally take about a minute for the engine to die if you shut off the fuel at the tank. But in this case, stated that the carburetor seemed to flood, which would indicate significant fuel supply.
Typically, if carburetor floods, no start situation.
Thu Apr 18, 2013 6:16 pm
May sound silly but -- that's what I am. A number of years ago there were reports of numerous Model T Fords loosing their magnetos due to a brand of oil that contained graphite (a conductor). OK the T's mag is part of the flywheel/tranny set up and running IN the oil. Just a divergent line of thought, bad seal and graphite in the oil or grease?
Never said I was sane -- just like to think way outside the box.
Thu Apr 18, 2013 7:15 pm
I didnt read all the post but my thoughts are ..... did you change the sparkplug wires? if so did you use a solid wire core or a graphite core? If graphite core wire is used It can damage the coil in a magneto. with graphite wires Voltage is built up in the coil till it burns through the primary coil to the secondary coil. I also have bought new coils that would work for a few minutes and guit. Found to made in china and defective. only other thing if coil and wires are good is that there is a short on the wires going to the points . Make shure that they are not touching anything. I dont know how you timed it. it may be slightly out of time. I have posted how I time a mag.
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