Subject:RE: Lightweight Sparkplugs Date:Tue Feb 3 19:00:31 2015
Response to:20215

So far as I know, the 165cc/175cc models have vertical sparkplugs and the 125cc models have sparkplugs angled to the rear.
The Harley lightweights started with the German DKW RT/125. Harley (and others) ended up with the rights to the design after WWII. The DKW 125cc had an angled plug, so the Harley 125cc copy had an angled plug.

That history is very well explained here -

The 165 was a Harley update of the original DKW design. Someone smarter than me can likely explain why the plug is vertical. Maybe the plug electrodes are more exposed in the combustion chamber?

I've been trying to educate myself on the lightweights. Consequently I've been studying a lot of photos. I've noticed that on some of the engines the sparkplug is angled to the rear while on others it is straight up. Can anyone explain this for me? Thanks