The 1984 K100
Rider's Handbook and the 1987
BMW K75/K100 Repair Manual specify non-resistor plugs. The 1988
BMW K1/K100RS Repair Manual specifies resistor plugs. Both the 1994 and 1995 K75
Rider's Handbook specify resistor plugs.
My K75 came with resistor plugs
and OEM plug wires with resistor caps. I've used resistor plugs as replacements. Electrode color at replacement is tan/grey. Performance is acceptable. Fuel mileage averages 50mpg.
Crazy Frog asserts
in a past post about K-bike spark plug and wire resistance that running
without sufficient resistance will damage the coils. Nothing is mentioned about damaging effects of resistance at ±10k ohm levels.
R. Fleisher,
in his comprehensive article on BMW bike ignition systems, asserts that excess resistance in the amounts being discussed here with Classic K-bikes
might have slight effect on both mileage and performance when plugs are at a marginal state. Resistance in the caps seems more effective for performance than resistance in the plugs, as I read his statements. Resistance in both may not be unnecessary, but he acknowledges that in some K-bikes both resistance caps and resistance plugs have been factory-installed together—the theory being those resistance levels slow electrode erosion while still allowing effective spark in the lean fuel mixture used by these bikes. Nowhere in his article did I read warning about excess resistance effects at these levels being damaging to the coils.
The exponents posting in this thread on both sides of this discussion are experienced riders and wrenchers. Personal experience will usually carry the day. What I'd like to read here is a forum member's explanation of why resistance of 6K ohm will not damage these coils but resistance of 10K–12K ohms
will damage them. From what have read so far, these coils might handle resistance levels like that with no significant effect.
My experience is that my bike seems to run ok with the current setup.