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Wild, Weird, Unexpected Electrical Problem/Solutio

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Andrew

05-09-2004 21:00:40




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Hi All!

I have a 1951 Allis Chalmers type B with which I have had a very puzzling electrical problem. I think I've solved it, but I wanted to add this experience to the knowledge bank at these archives.

For the record, I have a 12 volt system, alternator, ballast resistor and 6 volt coil.

The tractor was recently running really weak, then quit all together. I started tracing the problem back through the electrical system. No matter what I tried, I could not start the thing. I only ran the battery down from driving the starter. Then, I carefully pulled the cable off the coil to ensure I was getting a good spark there. I saw strong, inch-long sparks coming off the center lug of the coil - and suddenly, the tractor puffed to life! As long as I held the wire about an inch off of the coil, the tractor ran great! Too far, and the spark couldn't junp the gap and the tractor died. Too close or touching the coil - the tractor also died! I'm guessing that my voltage-dropping ballast resistor is bad (or poorly matched to the coil) and the removal of the cable from the coil provided the right amount of "resistance" via the gap jump to run the tractor at the appropriate spark voltage. Without the gap, the spark may have been arcing across the points, causing the real spark form the coil to the plugs to be weak.

Anyone else had this problem? I'm putting a new resistor on the tractor tomorrow - I'll report if that fixes the problem.

Andrew

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Steve in N.J.

05-11-2004 16:42:09




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 Re: Wild, Weird, Unexpected Electrical Problem/Sol in reply to Andrew, 05-09-2004 21:00:40  
Andrew,
Install a new contact set, and put a set of solid core wires on it. You'll be good to go...If you need any help or parts, drop us a line. Be glad to help you out....
Steve/B&B Custom Circuits



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Doug in OR

05-10-2004 12:07:20




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 Re: Wild, Weird, Unexpected Electrical Problem/Sol in reply to Andrew, 05-09-2004 21:00:40  
I've seen this problem before. What is happening is that with you pulling the wire from the plug, you are allowing the coil to develop a higher voltage and hotter spark. If my memory serves me right, the problem is either the coil or the condensor. Considering that the tractor eventually started (I'm presuming as the coil cooled) I would point a finger at the coil as the culprit. If you buy a new coil, get a 12 volt coil with the built-in resistor. This saves you the hassle of dealing with the ballast resistor.

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Andrew

05-10-2004 18:47:35




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 Re: Re: Wild, Weird, Unexpected Electrical Problem in reply to Doug in OR, 05-10-2004 12:07:20  
Well, this afternoon I tried several different things, none seemed to solve the problem. I tried the 6V coil with a different resistor, I bought a new 12V coil with internal resistor, I even traded out the condensor with the spare I keep on the shelf. I increased the point gap to 0.022. I even spoke sweet nothings into its distributor cap. In EVERY case, I could get the tractor running only when the coil plug wire is removed from the coil and forces the coil to fire a one-inch spark across the gap. I even showed my wife so I'd have a witness to this oddity. I'm stumped. Once started, it is possible to replace the wire into the coil and keep the tractor going, but it hesitates, misses, blats, and runs really rough. By throttling up and easing it into gear,I was able to move it closer to the house to work on it further this Saturday. But it is in no condition to mow the yard.

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Doug in OR

05-10-2004 19:34:03




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 Re: Re: Re: Wild, Weird, Unexpected Electrical Pro in reply to Andrew, 05-10-2004 18:47:35  
Check the following: Are the plug wires in good shape? Clean, and with no cracks or other such defects. Check the spark plugs. Are the insulators clean and in good shape? Last: Pull the plugs. Any excessive carbon?

Something in your ignition system is keeping your plugs from firing unless you apply an extra amount of voltage to them. Look at the above items and see if anything is amiss.



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steve

05-10-2004 19:38:22




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 Re: Re: Re: Re: Wild, Weird, Unexpected Electrical in reply to Doug in OR, 05-10-2004 19:34:03  
im with Doug, was just going to suggest getting a new set of copper wires (not high resistance carbon) and a new set of plugs. you appear to heed HIGH voltage to get it to fire.



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Andrew

05-12-2004 18:51:52




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 Re: Re: Re: Re: Re: Wild, Weird, Unexpected Electr in reply to steve, 05-10-2004 19:38:22  
Well, the experts were right! I purchased a set of four Autolite 295 plugs this afternoon, gapped them to 0.035, replaced the exisitng somewhat fouled set, and she cranked right up.

I didn't do this initially because I had just installed a set of CHAMPION plugs sometime last fall. Oh well, looks like a tune up to prevent refouling this set of plugs may very well be in my near future!

Thanks so much to all of you again.

Andrew

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Doug in OR

05-12-2004 19:16:13




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 Re: Re: Re: Re: Re: Re: Wild, Weird, Unexpected El in reply to Andrew, 05-12-2004 18:51:52  
Champions work, it is just that you have to go several heat ranges higher than recommended. I've always found that merely switching to Autolites did the trick for me.

Thanks for the followup. Many times I sit and wonder if my advise was worth a hoot.



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