Correct spark plugs for my 500 ?

[philward]

Great watch

Sent from my moto g(50) using Tapatalk

[davidcumbria]

[...] Run iridium in most of my bikes which definitely help starting but can’t see one for the 550.

Any new sparkplugs will help starting. Some in the German forum have tested iridium plugs but were not impressed. These plugs will do well in modern bikes however which run much leaner than our filthy beasts.

It's primarily about service life and gap change during that lifing to meet intervals in schedule as opposed to significant changes in performance of the plug.
Before these materials they were heading toward twin and triple earth type plugs for durability (typically toward 36,000 miles in car engines) ultimately superseeded by this type of plug with more resistant materials.

I have found empirically that The pin head electrode  in iridium plugs does produce better performance in some bikes. Less fouling and better idling and starting on all my two strokes. Notable better starting on my xt250 single which is a well known tricky starter. I wouldn’t waste my money buying them had I not seen irrefutable improvements in several fourstroke and two stroke engines versus new non iridium.  It’s not just about longevity it’s about the shape , power and consistency of the spark.

[Bryanj]

Stan was the travelling rep for a London firm near Wembley called Mobyke i think, the imported the rotary engined german bikes which the press wrecked the demos of(dkw?) Also did Marvin exhausts which were incredibly loud if you removed the baffle but being Italian the chrome fell off!