Spark Plug Caps

[Gibson]

While going over my bike I discovered the spark plug caps felt as though they had a loose feel to them. I've been investigating an intermittent misfire. I had gone over everything very carefully, but the previous owner mentioned that he had just replaced the wires and metal caps, so they were sort of overlooked. It turned out that the metal caps required the threaded on post that goes on the tip of the spark plugs. There was evidence of the spark arcing inside the cap. I put on threaded on tips and bike runs quite a bit better. I am surprised that it ran as well as it did given the circumstance. I do not think these metal plug covers are BMW OEM parts, but apparently some of these require the threaded tip, and some don't.
I ordered the NGK plastic resistor caps. They seem to be good quality and hold up well.

[Duane Ausherman]

The caps provided on all /2 bikes had those metal covered caps. Two pieces of sheet metal were crimped over to fasten them. The threaded screw to go into the spark plug wire was one of the characteristics too. I think that you have stock caps. You may see them here. http://tinyurl.com/hffve9u That cap was used because it reduced RF radiation from the ignition system to nearby cars that might have the radio on. Do you care?

In the SF bay area we had to remove all of them due to the high humidity getting in and shorting them out. I put on simple rubber caps called Sparkies and they were great, just not original. You may see them here. http://tinyurl.com/jg7ts2u

I think that your resistor caps will work just fine for you.

[Gibson]

Hi Duane, Your right. Don't care about radio interference noise. For late model airheads such as mine, I need to use 5k resistor cap to protect ignition. Points models should all use non resistor caps agreed. They run better!

[Duane Ausherman]

Yes, and that resister also does some good things. You really don't want me to go into the radio theory involved.

The Sparkys didn't have a resister and it was OK, but we would add one inline when using a timing light in order to get it to flash.