# Spark Tester



## RKDOC (Jun 20, 2006)

I was wondering if a two stroke and a four stroke have different voltages to the spark plug? I have two different spark testers that I use. I hook the clip end to the spark plug and the plug wire on the post of the tester, pull the rope and watch for spark. I have tried this on a two stroke and will see no spark. Take the plug out, squirt some gas in the plug hole and start the engine. On a four stroke I will always see a spark. (unless ignition is bad) Can anyone tell me why my tester will work on a four stroke and not on a two stroke? Also I have read that you should always test the spark with the spark plug installed. Some times When I have the plug out I clamp the alligator clip to the plug threads for the ground when I test for spark. Is this wrong?

Thanks for all your help and advise.


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## firemedic6451 (Nov 12, 2007)

When I test for spark on a 2 stroke, I usually slide a screw driver down beside the cylinder for a good ground. Then you use the spark tester hooked to the screwdriver. 
Some how the spark tester does not ground its self on a weedeater or a bloer like it does on a 4 cylinder.


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## jarheaddoc (Nov 11, 2007)

I believe those spark testers are designed to be added to the circuit, not create a different one. The plug should be installed for it to work properly. Not knowing the specific ignition you're testing, I would say that you've somehow bypassed the way it's designed to work. You've obviously got spark if the engine runs.


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## OptsyEagle (Jul 17, 2007)

I would not consider myself an expert on this but I cannot see why the 2stroke or 4stroke differences would require a different voltage to the spark plug. One needs enough voltage to the spark plug to generate a strong spark under a compression environment. So I would say if the engines compressions are the same, then the voltage should be the same (assuming same gaps, etc.).


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## RKDOC (Jun 20, 2006)

Thanks for the replys. When I hook the tester up I am hooking the aligator clip to the spark plug (still installed) the post of the tester is hooked to the plug wire. In my mind there should be no difference between the spark from a two stroke and a four stroke. All I know is that the tester will show no spark yet with gas in the plug hole it will fire. I have two diffrent testers and it does the same thing with both of them.

Thanks for the help


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## 30yearTech (Sep 14, 2006)

A very high intensity spark is sometimes almost invisible, although you can usually hear the crack or pop it makes, but that may be hard to hear with the plug installed and compression noise from the engine. You can usually pull the starter rope on a smaller engine a lot faster then you pull the rope on a larger mower engine. Try pulling the rope at a slower rate and see if you can see the spark through the tester.

There should be no difference between the 2 cycle and 4 cycle as far as the spark generated, both ignition system pretty much operate the same with regards as to how they generate a spark.


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## RKDOC (Jun 20, 2006)

Thanks 30 year. Is it all right to test the spark with the plug removed? I read somewhere that you should not do that.

Thanks.


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## 30yearTech (Sep 14, 2006)

I test it both ways, first without the plug and then with the plug. But thats just what I do.


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## OptsyEagle (Jul 17, 2007)

I made my own spark tester by taking a piece of wood (U shaped cut with a jig saw) and drilling a hole through it at the bottom of the U. I then put a 1/4" bolt through it. Above the bolt (or at the top of the U ends) is a piece of sheet metal. I then connected a wire with an aligator clip to this sheet metal. I simply connect the aligator clip to the ground and the plug boot to the other end of the bolt. With the bolt screwed in to the gap I want (gap is between other end of bolt and sheet metal), let say 3/8" or so, I turn over the engine and if I get spark, I know it is strong enough to jump the gap I have created.

Of course with this method the actual spark plug is not used.


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