Quick and dirty spark tester

[Grimly]

Made me think of the Suzuki service bulletin for GT750, how to do a rudimentary test of a coil without the Suzuki testing equipment.
Clip off the whole arm of the spark plug and check out how it sparks.
Spark should at least reach the side of the plug, preferrably a strong blue spark.
Yellow spark is already considered weak and a weak yellow spark means bad coil.

While waiting for a spark tester to arrive, reading the above led me to try this.
To make it more convenient, I utilised two croc clips and a foot of insulated wire. The plug is held in one end and the other clip is grounded to the fins.
It works well. Of course, it tells me nothing about how the spark behaves under cylinder pressure, but a healthy blue/white spark leaping 5 or 6mm across the end of the mullered plug leads to think there's not much wrong there.

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[93Bandit]

"clip off the whole arm of the spark plug"

Does he mean cut off the side electrode/strap?

 

[rphillips]

Clip off the ground arm of spark plug? Did you ever hear of surface gap spark plugs? Isn't that what they are?

 

[Grimly]

a healthy blue/white spark leaping 5 or 6mm across the end of the mullered plug leads to think there's not much wrong there.

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Oh, how easily fooled I was.
Today, I've just taken delivery of a spark-gap tester. It revealed that 1&4 coil was putting out 20+kV, but coil 2&3 was only about 10kV-ish. Hard to be sure, as spark gap varies with temp and humidity, but the distinct difference was there. The failing cylinders were firing ok, but I knew there was something not quite right, and in the past I've usually just cleaned up the LT connections and restored smoothness.
I found the culprit almost immediately, a crusty wire crimp in a bullet connector - remade that and re-tested. All is better now.
Also fitted a set of Denso W22TT plugs, just for the sake of it.
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[Rijko]

"clip off the whole arm of the spark plug"

Does he mean cut off the side electrode/strap?

Yes

source : http://www.ozebook.com/compendium/techbuls/SerBulletin General Index plus 1-9.pdf

 

[93Bandit]

Interesting.







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