So an old timer taught me this trick. I was at a county fair looking at all the old tractors. Got talking to one of the older fellas that had a 1942 Johndeere LA with a flathead 2 banger in it. He fired it up for me, and it dropped a cylinder, but kept running on one cylinder. He says "well shoot", walks over pulls the cap off it, gets it close enough that the spark starts jumping, and holds it there for a couple seconds. Low and behold the plug starts firing again! he replaces the cap, and all is well. So i was working on my ol 42 dodge, getting it outta hibernation. Get it running, but its running rough. Find out its the 2nd cylinder thats dead. I remember the trick and decide to give it a go. with it running, i yanked the cap off, and set it so that the spark has to jump a 1/4 inch gap or so. After bout 4 seconds, that cylinder picks up again. Set the wire back on, and it drops. Took it back off, and made it jump again for about a minute, set it on, and it kept going. Damndest thing huh? So there ya go. Try that next time you foul a plug.
This is kinda the theroy behind a resistor plug. build a resistance right in the plug so that by time the voltage builds up to overcome that, it's a fatter spark.
go ahead..try that with a cracked cap,that you don't know is cracked...ask me how i know...i swear i can still taste my fillings !!
Funny, I got poped with a MSD set up once. It just kept hittin me for seemed like forever. I hit my head on the hood too.
Pulling the wire out of the cap forces the coil to try its best at jumping the gap and increases the energy to the spark plug ( like someone above said). The same trick works for a flooded engine as well just pull the coil wire back from the cap and it will increase spark delivery to all the cylinders etc. A interesting fact of spark ignition is that the coil ONLY supplies what is needed. Example : A normal engine with factory compression ratio and a proper air fuel mixture only needs from 5,000 to 8,000 volts to ignite the air fuel mixture. The coil has a reserve voltage capability of less say 20,000 volts. Properly tuned it will use only 5-8,000, when accelerated under load it may need 8-12,000 volts and the rest of the reserve is there for wear and tear of parts, air leaks ( takes more) and just general driving loads etc. Install a big ole yellow 50,000 volts coil and it will still use only 5-8,000 volts.
When I was farming part time, I had 15 John Deere two cylinders. Many of them hand start. I got "Almost Kilt" from an old magnito doing that once.... Never did that again, and not sure I ever fully recovered either.....YIKES...
Everyone has the correct answer here, it's basically how much potential your coil has, bigger gaps need more power, increasing the gap increases the power. Really easy to see on a scope if you ever get a chance. Every coil should produce more than it ever really needs... That being said I'd just rather pull a plug and clean it, since I hate getting zapped. Points distributor=not too bad, leaky wires=kinda tingly, HEI=WOWEE!, coil pack/distributor-less ignition=I think I'll take 5!
If it does really work, this might be the mechanism... 1) A wet or carbon fouled plug just gently bleeds off the energy and you get no spark at the gap. 2) Making it jump from wire to plug provided the power more in spurts, so the voltage surges a bit and, along with it, the current. 3) That surge in current may be enough to burn up or break the little carbon track or vaporize of a bit of fuel. 4) Then the gap cleaner and more free to spark like as should without the energy being bled off.
Correct, and there's more to the story. The gasoline or oil which fouled the plug gets between the insulator and plug shell and creates a ground path that allows rising current to go to ground without jumping the gap. Putting a gap between the plug and cap eliminates that path, and causes the voltage to rise sufficiently to jump that gap and the plug gap. Bob
x2 for wedged reply. before ford did away with dist on ot cars. we (at the dealership) would pull the coil wire off the cap and lay it near the coil terminal at the cap forcing the spark to jump the gap, increasing the energy to the plugs and getting fuel fouled flooded engines to start. it was alot easier than pushing cars that wouldnt start when the tow truck would drop them off in the lot instead of in the building. since everything is coil on plug or coil packs, we rarely see flooded engines anf this trick has kinda gotten lost. some of the younger techs i work with have never seen this done.
Interesting. I'm kinda partial to just pulling the plug and cleaning it off with a wire brush or something. I really hate getting shocked. Good story though.
To say it a bit differently, when the current flows through the primary of the coil (points closed) it builds a magnetic field around it. When the points open the magnetic field in the primary colapses and induces voltage in the secondary winding of the coil. The voltage in the secondary winding builds until it finds a path to ground where it then drains the voltage. Ideally the energy built in the secondary will find ground by jumping the gap in the sparkplug. However if the energy can find another way to ground it will take that path of least resistance. If there is a foul in the plug then the fouling will bleed the energy from the secondary of the coil before it has a chance to build to a leval that will jump the spark plug gap. By holding the wire off the plug it allows the energy in the coil to build to a leval that it will finally jump the gap you have made and dissipated energy both at the plug gap and the fouling. Remember that this is a series curcuit so what goes through the artifical gap will also have to go through the spark plug. If it works then the combustion process will hopefully burn off the fouling of the plug and things will be good again. lg no neat sig line
That trick works for a while, but sooner or later you will have to pull the plug. And don't try it with electronic ignition, the spark will jump around in the cap and fire the wrong plugs. It can also damage the EI unit.
I am continually amazed by the unique topics like this and the amount of knowledge that is on the HAMB!
Don't pull it outa the "Cap" ,,pull the wire offa the spark plug ,( unless you have a Hemi ) ,,,thats why Snap-On,,and all the others have made insulated plug wire pliers for the las 75 years ,,i've been doing that since the '50's ,,werks no mater what kinda ignition you might have ,,
Next time you try it set up a camera and post the YouTube video of what happens, there has been a lack of comedy around here lately.
I recall a spark gap device you could plug into a coil wire to cause this elevated voltage on all cylinders at all times. Sold as a magic power-economy- booster.
I always pull them at the cap. I'd rather be holding a "dead" wire when the spark isn't jumping than a "live" one. Larry T
I just pull the offending plug and check it, I then clean all of them. You're gonna end up needing to do it sooner or later.
The Jalopy Journal
