color of spark

[badgertom]

I recently posted a question regarding the poor starting of my 1982 r65. I got some good responses. Among other suggestions was to test the coil. I tested the coils primary and secondary circuits and all seems within range. Then I tested the spark across the spark plug and found that instead of a fat blue spark I got a an amber spark. I then used a spark tester which allowed me to read the voltage across the gap at about 25000 ( with an amber spark) So what does that mean...if I get an amber and not a blue spark. Is the strength of the spark in question? Also, would this cause the bike to start poorly?

[Bob_Roller]

The spark should be a blue-white color .

Normal output for the electronic ignition system is around 35,000 volts .

In a fuel air mixture and a pressure of around 145 psi, the spark may not be up to jumping across the gap at the spark plug as it should .

What color is your coil, an OEM gray and black, or an OEM red type ?

If you have the gray and black, replace it as soon as you can, it's a known problem part .

The case cracks and will usually give you problems in damp conditions .

My original OEM black and gray coil failed at 23,000 miles, replaced it with an OEM red coil, it lasted around 40,000 miles .

With my multimeter, I got a value of 1.6 ohms for the primary, my meter was not correct, it was off, the value of the primary was really .6 ohms, kinda hard to troubleshoot a problem, when your test equipment is faulty .

I installed a Dyna brown coil about 9 years ago .

A weak coil will cause hard starting, especially the first cold start of the day .

What resistance values did you get for the primary and secondary circuits of the coil ?

Testing needs to be done with all of the wires disconnected .

[montmil]

This is the OE Bosch Crack-O-Matic ignition coil off my 1981 R65. Note the small cracks in the end of the coil. Hidden under heavy dust, they were invisible without a wipe down and close inspection.

A Dyna Brown coil cured all ills: poor starting, engine missing in damp weather, weak sparks. Getcha one.



D'oh. Just noticed this is my 5000th post to this forum. My wife says I talk a lot, too.

[Barry]

Although it's the perceived wisdom that a yellow/orange spark is weak  I have some trouble equating that with the fact that you have been able to test the spark to 25000 volts. Only approximately 10 - 12000 volts is actually needed. The previous points ignition system wasn't even capable of 25,000 volts and that worked just fine.

So although I don't have a lot to base it on I think it's possible that your spark colour may be misleading. I have seen ignition systems produce a yellow/orange spark and work OK. Maybe the spark colour can be influenced by plug deposits or atmospheric conditions.

[montmil]

If you have the spark plug grounded to the cylinder and in ambient workshop air, the color should be a blue-white. The orange-y color spark will be even weaker under operational compression.

Have you tried fresh plugs? Tested the wire leads and plug caps? Are these leads and caps 30+year OE?

Keep checking. It's usually something simple. If Bavarian farm boys can fix these bikes, so can you.

[Barry]

The orange-y color spark will be even weaker under operational compression.

As I said that is the perceived wisdom, I'm just questioning it that's all.  We have always known that the spark has to be blue but do we really understand why that is ?  The problem is I can't find anything to explain scientifically why the yellow/orange color of ionised air defines a spark as being weak especially when it's a 25,000 volts spark.

I did find one article that claimed it's an old wives tale but I'm not convinced either way by just one reference.

http://www.briggsandstratton.com/support/frequently-asked-questions/Ignition%20System%20Theory%20and%20Testing/