Ok here we go.. If you look at a older shovelhead and were the plug is situated in the combustion chamber it sits way down a hole. You can't buy a plug to get it more closer to the chamber without it sticking in so far that it will hit your piston.
So I took a newer style of plug and spaced it back just enough to leave lots of room between the piston when it comes up thus putting the plug further into the chamber.
If you look at the picture of the cyl heads in regard to each other you will notice where the corrected plug sits verses the stock plug.
Also I use a BPR plug by NGK. This is a plug witch protrudes out further than a non P type plug giving it a further reach into the chamber without risking contact to the piston.
All this dose is put your spark closer to the action of your chamber.
So... Take the part #730-2440 witch is a NAPA part. The only reason I need this is to cut off the top of it so I can thread it onto the NEW plug # NGK BPR5ES to shorted it just enough to put it out of harms way.
You need to cut off the crush washer off the spark plug only and put a dab of thread sealant for your new threaded spacer. Use the new crush washer and put it in place after you put your new spacer on. Remember to use never cease on the threads that are now showing. You should now have a plug that looks like the picture shown.
I hope this all makes sense and helps the performance and start ups on kick bikes! I know it made a big difference on all of my older style cyl head shovels.
Thanks for looking!