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Checking spark quality

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Author  [Modern View]

08-12-2017 09:59:20

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Following 75 tips it says to use an old plug and open gap to 1/4 inch to see if spark jumps gap. The spark I get at each plug wire arcs to side of electrode and not to tip. 1/4" gap makes electrode not parallel. What am I missing?

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08-12-2017 17:48:49

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 Re: Checking spark quality in reply to swhockett, 08-12-2017 09:59:20  
If its jumping from the center tip to the metal body That's about .150 you gap is .250 its gonna take the path of least resistance. ... If its going down the ceramic then jumping across you have a contaminated plug.
Another type of small engine spark checker is machine to 1/4" gap like the one in this pix (Stens 750-018)... Its a basic conventional spark checker... Invest in a fixed checker are a adjustable forgo the folklore of rolling your own from a old spark plug it will beat you up...

Don't confuse this one with a Electronic Ignition Spark Tester (HEI) it looks almost the same but but a totally different animal. On a HEI tester the center electrode is buried deep into the center ceramic using somewere around 1/2 gap....

Adjustable works on conventional and HEI...

The ones that light have some value but not a true spark checker in my opinion. There are some that do light and have a fixed gap I dont' know what to look for in one of'em unless I had it in my hand.

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08-12-2017 17:23:58

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 Re: Checking spark quality in reply to swhockett, 08-12-2017 09:59:20  
Quoting Removed, click Modern View to see

Rather than buy the big plug just go buy the correct tool.

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08-12-2017 17:15:15

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 Re: Checking spark quality in reply to swhockett, 08-12-2017 09:59:20  
Use a big plug like a D16 Champion.

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08-12-2017 10:41:36

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 Re: Checking spark quality in reply to swhockett, 08-12-2017 09:59:20  
The spark will jump the shortest distance. If the gap to the tip is further away then the distance to the side it will go to the side. Close the gap some and try it again or do as Caryc suggested and purchase a spark tester.


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08-12-2017 10:15:25

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 Re: Checking spark quality in reply to swhockett, 08-12-2017 09:59:20  
What you're missing is using the correct tool for the job. It's only a few bucks at your auto parts store.

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Bill Crowell

08-12-2017 12:04:37

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 Re: Checking spark quality in reply to Caryc, 08-12-2017 10:15:25  
There are two kinds of in-line spark testers: neon bulb and electrode. I think both are useful. The neon bulb type tells you at a glance if you have any spark at all, but even if spark is present it has also gotta be strong enough. The guys on here say that the electrode-type tester, with the electrodes set at 1/4" separation, tests whether or not your spark has the necessary strength.

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Bruce (VA)

08-12-2017 12:23:02

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 Re: Checking spark quality in reply to Bill Crowell, 08-12-2017 12:04:37  
The problem w/ the bulb is too many folks see it flash & think they have spark. It takes 22k volts or so to produce a spark that will jump 1/4" in open air. I'd guess that you can see a flash of light at about half that voltage. And that will not produce a spark in the cylinder.

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