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jumping spark plug gap

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norman macknair

11-07-2006 12:42:40




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I have had this problem on things from motorcycles to tractors and am curious if anyone else has figured out why. You know when your tractor is missing and you pull the wire away from the plug to to see which plug is missing, I find that sometimes if you make the spark jump like an 1/8 inch the engine stops missing and plug fires. but if you plug back in it misses. how do I fix this? new plugs work for a day or two. Thanks

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dan hill

01-25-2007 03:12:45




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 Re: jumping spark plug gap in reply to norman macknair, 11-07-2006 12:42:40  
If you would let the spark jump a bit longer the carbon would burn off the nose of the insulator and the plug would fire normally.Heres what happens,The spark runs down the carbon on the insulator instead of jumping the gap.I use a Model T coil to check distributor caps and rotors.A carboned plug insulator will show up when tested this way.Carbon fouled plugs can be cleaned by soaking in a jar of acetone.Put a cover on the jar.Some gasoline is prone to carbon fouling.

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Bob

11-10-2006 08:14:06




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 Spark Intensifiers in reply to norman macknair, 11-07-2006 12:42:40  
This question comes up every now and then, around here. Below is a link to some REALLY fancy spark intensifiers. (I have posted this several times before.)



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massey 44

11-08-2006 15:24:21




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 Re: jumping spark plug gap in reply to norman macknair, 11-07-2006 12:42:40  
Try changing the plug wire. If you have a gap in your plug wire the increased voltage caused by holding the wire off the plug causes the spark to jump the gap in the wire then delievering it to your plug!!



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noncompos

11-07-2006 20:12:46




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 Re: jumping spark plug gap in reply to norman macknair, 11-07-2006 12:42:40  
Back in the days when money to overhaul engines was hard to come by (and when we were afraid to take them apart for fear of what we"d find) we rigged jump-sparks to keep our oil burners going, as well as using the hottest plugs we could find that fit in the holes...it was as normal as a boot or an inner liner in a tire...ahhh, the good ? old days...



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Gene Davis (GA)

11-09-2006 18:46:46




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 Re: jumping spark plug gap in reply to noncompos, 11-07-2006 20:12:46  
Way back in the stone ages, people would have a car, truck, or even a tractor that oil fouled the plug on maybe 1 or 2 cylinders and they used a thing called a "buttom jumper". They took a 4 hole button and cut the wire in two parts and threaded the stripped wire into one side of the button holes and twisted it together so it would stay on the wire, then did the same on the other side with the rest of the plug wire and it createwd about 1/4-1/2 inch gap depending on the diameter of the button. It sure was cute looking running at night. Looked like they had an engine compartment full of fireflies and absolutely so much radio static that no body used their A M car radios. But it made many a trip to town for the pooe farm family on Saturday..

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Ol Chief

11-07-2006 18:36:19




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 Re: jumping spark plug gap in reply to norman macknair, 11-07-2006 12:42:40  
Just an old bikers trick.In 1949 I bought a new Harley Davidson 74 De Lux.Did not know anything about bikes.Seems that running slow in traffic those engines would foul the plug in the back cylinder.I was a long way from home and the engine went down to only one cylinder working \. You really don't want to try to run a Harley on one cylinder,God Awful.Well no tools onboard and scratching my head pulled over with puzzlement what to do.Shortly a gang of older bikers coming the other way saw me and all pulled over. One old guy came over and asked me why stopped.I told him and without saying anythig to me asked the group who had a book of matches.I was puzzled.He got a matchbox and tore off the cover then unscrewed the terminal nut on the spark plug and forced the cardboard onto the thread and replaced the nut then stuck the cardboard into the wire terminal allowing about a half inch gap between the wire and the plug.OK, fire it up kid!I did and she went off immeditely on both cylinders.Then said go on and runner about 15 or 20 miles like that and it ill cleaner up.Since then always carried a book of matches.

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Hermit

11-07-2006 17:01:30




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 Re: jumping spark plug gap in reply to norman macknair, 11-07-2006 12:42:40  
The voltage produced by the coil is based on the largest gap found in the ignition system. For example if the largest gap is a spark plug gap of .030, the coil will produce 4-5000 volts to overcome that gap. If your plug is fouled out, your coil will produce much less since it doesn't have to overcome a gap just go through the fouled out part to ground. When you remove a plug wire and hold it 1/8 inch away, the largest gap is now the 1/8 inch (.125) and the coil will produce 10-15000 volts to overcome that gap. That increase in voltage will also allow a spark to jump the spark plug gap instead of going totally to ground through the fouled out area, making the engine run better. When you put the plug wire back on, you're back to having a fouled out plug with the electricity going to ground and not making a spark. If your new plugs are only lasting a day or two, you need to find out why they're fouling out. There are many diagnostic pictures of spark plugs on the internet to help you determine the problem. Good luck.

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norman macknair

11-13-2006 17:54:07




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 Re: jumping spark plug gap in reply to Hermit, 11-07-2006 17:01:30  
I understand what you are saying about the coil producing the amount of power it takes, that is the first good answer I have ever received also. That leads to another question, why wouldn't you just "over" gap the the plug from the start. if specs call for .20 why not make it .50?
Thank you
Norm



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Hermit

11-16-2006 17:17:30




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 Re: jumping spark plug gap in reply to norman macknair, 11-13-2006 17:54:07  
Here's some more engine theory for you. There's a couple of reasons opening the gap may not work.

1. If you have a problem with a cylinder, once a plug becomes fouled because of gas or oil or deposits, the electrons flowing from the coil don't build up voltage to jump the spark gap but bleed away to the ground. That's why an external method of increasing the voltage, like holding the plug wire off the spark plug, is required to get the spark plug to fire. It allows the voltage to build up and not bleed away.

2. The coil is designed to push only a certain number of electrons through the spark plug wire when the magnetic field collapes. And these limited electrons must be balanced between two different spark patterns making up the ignition of the fuel/air mixture, the initial spark and the continuous spark. The initial spark occurs when the points open and the field collapes. The voltage spike produced will overcome the spark gap and compression in the cylinder, around 5000 volts. Then once the initial spark has occurred and the field continues to collape, a continuous spark occurs requiring a voltage around 2000 volts for 1-2 milliseconds. Less voltage is required on the continuous spark because the initial spark creates an ionization path for the electrons, making it easier for the electrons to jump the gap. The continuous spark is required for a more complete combustion and more engine efficiency. There's not just one big spark from the coil. That wouldn't allow for complete combustion, robbing the engine of power.

Have fun.

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B-maniac

11-07-2006 18:30:19




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 Re: jumping spark plug gap in reply to Hermit, 11-07-2006 17:01:30  
Hats off to you ,Hermit! We learned about this phenomena of electrical physics back in '68 when in high school auto shop. You are the first one I've seen get this right and you did a damn good job of describing it to him too. "B"



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old

11-07-2006 14:06:51




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 Re: jumping spark plug gap in reply to norman macknair, 11-07-2006 12:42:40  
What is happening is you have some thing that causes the plugs to foul. You either need to find the problem. As in running to rich or burning oil. Or you can try a hotter plug.



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