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Mysterious Dissappearing Spark

L

Lamentations

New User
I seem to have no spark.
If I remove one of the plug wires at the distributor, & put a screwdriver in, it will rest such that there is about a 1/16” gap to the exhaust manifold.
If I then crank the engine, I can see a healthy spark.
So far,so good…but, if I connect a plug wire & ground the plug,,,no spark.
Brand new wires & plugs, plus I tried a couple wires I pulled from another car.

This tractor was running OK the other day.

I replaced points, condenser, rotor, & cap as well as wires & plugs.

Any ideas?
Thanks
 

Are the new wires actually making contact in the sockets of the distributor cap? Are the plug wire terminal ends installed properly?
 
Well since you have spark with out the plugs but do not have spark with the plugs do you happen to have gotten a bad set of plugs. Have you tried the old one to see if they have spark?? Is the spark you get from the plug wires a white/blue spark and will if jump a 1/4 inch gap. If it isn't all of those then you have a problem. Also might help us help you if we knew what your working on. New points could be gaped wrong or need the oil wiped off of them
 
If a plug wire end or screwdriver etc out a cap terminal is placed within about 3/16 from steel you should see a good visible blue spark and thats the goal, NOT a faint thin wimpy yellow spark.

Soooooooo if you can get such using a wire or screwdriver etc out the cap BUT theres no spark with a good plug attached and well grounded, sounds like EITHER the plug wire or plug may be bad.

See if you get a good visible blue spark if you hold the plug wire end to within 3/16 of steel??? if so but theres no spark using a well grounded plug, the plug must be bad. Try swapping different wires and plugs to isolate if its a plug or wire problem.

Since you replaced points and condensor Id wonder if the new condensor is good and/or the points are gapped proper and theres no shorts in the points or points and condensor wiring. Try it with the old condensor n see what happens

John T
 
Ford 3000
It was running with these plugs.
I shut it down one day, & the next day when I went to start it, this problem showed up.
The spark I get is on the weak side.
I forgot to mention there's a brand new coil too.
 
Maybe the plugs got fouled and that's causing all the problems? Not so much on a 4 stroke but I've seen brand new plugs foul right after being put in 2 stroke dirt bikes. The split fire plugs that were supposed to be so good, were the absolute worst for fouling. Dave
 
Well one of your problems is the plug wires. Tractor need true copper wire plug wires and will cause that type of problem is you do not have them
 
Test it with a 1/4" gap, not a 1/16" gap. If it will jump a 1/4" and make a blue spark in free air, then you've got the 40,000 plus volts needed to fire a plug under compression in a fuel-air mix.

Electricity follows the easiest path to ground. When you tested with a 1/16" gap, it barely needed 30,000 volts to fire. When you hooked in the plug, it obviously called for higher voltage, and the electric charge ran elsewhere and out of sight. If you did the test inside a dark garage, you might see where it's making its way to ground. Usually impossible to see in daylight (but you might hear it). And there's also the remote possiblity that the plug has no continuity, or wire the same, and your coil cannot generate high enough voltage to travel through it.

That's why you test with a 1/4" gap. That, at least tells you there's more then enough voltage available to fire under most conditions.
 
How about wrong coil? Or using external resistance when not necessary. I say resistance because it can be in the wire(which looks normal)and not like a resistor.
 
I'll try that when I get into town next.
I got the new plug wires at the Ford dealership,
you'd think they would know what they're doing,
but I'm not getting that feeling.
 
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