Pink spark??

[rapcom]

For a variety of perfectly good reasons, this evening I removed my four spark plugs (twin plug heads) to check the sparks. With all four plugs mounted in my special jig (a piece of aluminium angle with four plug-threaded holes in, with an earth lead with croc clip), I was puzzled to note that I had three blue sparks and one with a decidedly pinkish hue. The two twin-output coils are identical, the leads are all the same brand and almost the same length, appear to be undamaged, and all the plug caps and spark plugs are identical. The pink spark always comes from one particular coil output.
Can anyone give me a clue as to why I have one pink spark?

 

[ossie]

its probably the female plug????
OSSIE

 

[Albervin]

Potassium burns pink. Not sure if that is a red herring though..... If you adjust the gap does the spark change colour? Check the point at which the HT lead connects to the coil for any sign of contamination.

 

[John Appleton]

Dick!!!! I prefered the one about the longer pad bolt.

John.

 

[timetraveller]

I have a spark tester which is nothing more elaborate than a variable gap. Probably a Gunson’s product but I have not gone out to the shed to check. It would be trivial to check the distance that each spark will jump, just to check that there is nothing wrong with one of the outputs. If they are all the same then contamination of the plug, a ‘strange’ lead or other cause will have to be looked for. If the problem has not been sorted by the next time we meet, remind me and I will bring it over.

 

[roy the mechanic]

i wold reccomend testing the ht leads+ caps with an ohm meter ,leads should be around 10k per metre caps max 5k if this checks out the coil is on its way to the happy hunting ground.

 

[rapcom]

As I always hate it when someone starts a thread and then never bothers to give any results, I thought I had better update my query about a pink spark. Timetravellers post about the variable gap spark tester reminded me that I too had one in my toolbox, so I conducted a series of tests with it. With and without suppressed plug caps, with kickstart or electric start, old ignition switch or a separate new switch, you can all imagine the permutations. The end result was that one of my coils was consistently weaker than the other in every test. I have accordingly ordered two new high performance coils. When they arrive, a new series of tests will be carried out. Watch this space.....

 

[BigEd]

Thanks for the update. Some "query" threads just tail off with nobody knowing if a solution has been found.

As I always hate it when someone starts a thread and then never bothers to give any results, I thought I had better update my query about a pink spark. .......... .....

 

[roy the mechanic]

hi, look at answer no.6-looks like a coil is going to the happy hunting ground. looking forward to sunday! roy.

 

[rapcom]

As promised, an update on the saga of the pink spark. After my testing, and the responses on this forum, I decided to buy new coils. Research and advice from Francois and other experts indicates that my Grosset ignition needs 3 to 5 ohm coils, with 5 ohm being optimal, and the DynaCoil site also advised 5 ohm as being suitable for road use. I accordingly ordered a pair of DynaCoil "DC8-1" 5 ohm coils. After a wait of three weeks for them to arrive from the USA, comparative testing with the Gunson variable-gap tester showed an increase in reliable gap jumping from 2mm to 12mm, and of the four sparks, none of them were pink....
The bike now starts better, runs strongly, and I'm hoping that my ignition problems are solved.