My owners manual states that a H-D 6R12 spark plug is to be used with an 2003 RKC. The gap is from 0.038 - 0.043. Why such a variance in gap? What is the spot on gap? I know with my 1965 sportster with points, plug gap had to be closer than that.

Randy

 

Because if you are in that range it don't madder.

 

The difference in gap is only .005. that isn't very much. I like to set plugs on the low side to account for erosion of the ground strap and electrode.

 

Set it to .040 and forget about it.

 

I've used the .040" forever (since '99), works all day long.

 

This, the range you read about is minimum/maximum. Split it at .040" and ride.