From Fred B. - Just wanted to share a
little something I just discovered about spark plugs. As you
recall I've been doing the old "Jet n Plug" two step on my bike
and needed a good stock of plugs. I live in a small town that does
not stock most Japanese plugs(ie. NGK and ND) except those that
fit tractors, hay bailers, or some other farm implement. Anyway, I
went over to my local parts house and bought a set of Champion
plugs that were cross referenced for my bike. The parts guy said
he double checked and they were exact matches. I got home and
pulled them out of the box to set the gap and the first thing I
discovered was that they were a different socket size(can't
remember which). Next was that they were type that had terminal
caps on them for the automotive type caps not the threaded stud
type for the bike. I had to use vise grips to get them off. Now
that I was totally aggrivated I decided to check the resistor
value and compare them to new NGK plugs. What a surprise! They
varied from 30k ohms to 80k ohms while every one of the NGK's read
5k ohms. Needless to say they went into the trash. The morale of
the story is: Use only the plug recommened by the bike
manufacturer!
Randy's comments: Fred B's experience had me curious, so I ordered 4 plugs
for my 95 Nighthawk 750 from Comp Acc in Ohio. I received two in
Honda boxes and two in NGK boxes. When I opened the boxes, all
four were NGK DPR8EA-9. I checked the resistance, and found a low
of 4.8K ohms and a high of 5.8 K ohms. I guess 5K +/- 20% is
acceptable. So what did we learn? NGK makes Honda plugs, and they
appear to have a better quality control than Champion. Now, does
anyone know if running plugs with a wide variation in resistance
affects engine performance?