Fuzzy black sparkplugs

[michael]

Just installed the rebuilt heads on my 1978 R100/7. Installed new rings at the same time. All seams to have went well. After 150 miles on new plugs they are fuzzy black. I think this indicates a rich mixture? Where do I start?

[Ken in Oklahoma]

Just installed the rebuilt heads on my 1978 R100/7. Installed new rings at the same time. All seams to have went well. After 150 miles on new plugs they are fuzzy black. I think this indicates a rich mixture? Where do I start?

I can think of a couple places to start. One would be to check the float level settings on your carbs. This is slightly messy, but easy to do. With the petcocks turned off you remove the float bowl. Then, holding the float upwards with your finger you turn on the fuel tap. Then you slowly lower the float and note the point at which the gas starts flowing. That point should be when the horizontal seam on the float is parallel (level) to the bottom of the carb body. If not correct you will need to pull the pivot pin and bend a brass tab on the float.

As an aside, I should note here that if your floats are old they may be heavy from gas having wicked into the float foam. This will cause no end of vexation in trying to get the float level. Since you haven't complained about the carb leaking gas your floats may be OK. But if they're not you may end up chasing your tail for a long time--that is until you buy new floats. Cheap, highly accurate, digital scales are available at your favorite office supply store.

The discussion of your problem may evolve to questions about your jetting, needles, and needle position. Unless your engine is modified, usually the stock jet selection will serve you well. Wrong jetting could result in an over rich condition, but without knowing what your jetting is you're shooting from the hip.

Aside from carb discussions, unseated rings come to mind. How did you do your "break in"? Did you oil the compression rings during reassembly? Do you have any indications of burning oil? Is your bike smoking?



Ken