Several commentors stated your indexing your plugs. Are you indexing to the intake valves?

 

Yeah not to hyjack this thread either but lets hear more about 'Indexing' since its supposed to be more about that than brand type the OP was inquiring about....

 

Yes, open side of the gap facing the intake valve. Indexing and side gap, aka trimming the ground strap, unshrouds the spark promoting hotter quicker flame front propogation and a self-cleaning condition because every A/F charge "washes" through the open gap. I've done it with Stock HD 6R12, colder HD 10R12, and Autolite 4163 all about the same results. Not necessarily a big power gain in a twin but much smoother idle and acceleration.

 

So are the HD head threads cut differently or is it the spark plug threads are so random? How do you know?

 

 

Good article in the link. So where can we get indexing washers from?

 

Probably a little of both, its rather rare for a blueprint to dictate that a thread starts in a specific location, even so tolerance would still be a factor preventing perfect index alignment out of the box.

Good article in the link. So where can we get indexing washers from?
http://youroilshop.com/plugs.htm
http://www.debrix.com/SPARK-PLUG-IND...p/3-271-mw.htm
http://www.sudco.com/spark.html#wash (bottom of page)
http://www.thunderproducts.com/Spark...g%20Washer.htm (not sure if these are 12mm)
http://www.jacobselectronics.com.au/accessories.htm
http://www.zippersperformance.com/ca...=583&prod=2280
http://www.nrhsperformance.com/partsignition.shtml (bottom of page)

 

Thanks for the info, as always your very helpful.....

 

As far as I've known indexing, it's not as much "getting the perfect path" for the spark to hit the flame front, but rather just not allowing the ground bar to barricade (shield) it from the fuel. In other words, there is margin for error.
I've seen a set of plugs screwed into the same hole and index themselves in six different directions, so evidently they are run randomly thru assembly in regards to that.

 

Plugs will indeed change the anti knock feature inside of the ECM. This really does exists, all one needs to do is ask any decent tuner. On Delphi EFI bikes... one will notice if they pull the plugs, hook a wire to one and spin the engine... the spark will try a few times and die with no spark. This is because the plugs do not see the correct resistance (compression makes it harder to fire a plug than in free air).and kills the plug firing.

I think any 'normal' type plug is OK. I simply run HD plugs because the dealer is close.