Spark Plugs Dommie

 If it has an aluminium head   Champion N5   or  NGK  B6ES.  would be a starting point .

Norton Twin Restoration by Roy Bacon listed recommendation  for 500,600,650 std 1956-65, KLG FE80, Lodge2HLN, Champion N5 and NGK B5ES.

Plugs come with a gap set around 0.025” which is correct for coil ignition.

For magneto ignition it should be reduced to 0.015” or 0.018”.

Yes to N5 for 88 & 99's, so where did Champion N4 for 650's come from, apart from me?

PS: on another thread, my 59 ES2 engine  (In the build)  does not have an oil seal in the drive side. I based my response on this alone. 

Hi Neil,  A hard ridden 650SS  should  keep N4's  hot and clean, The N4 plug in a high comp 600 Nomad blasting through the Arizona desert  will work well.  The same  bikes  pootling around to classic events or  used  for commuting and touring  will  usually soot them up enough to make the next  cold start difficult.  But every bike is in a different mechanical state and tune  with varying fuels  so there is plenty of scope for finding something unusual works for you.

Page 80 in the Compendium shows a very useful spark plugs for Nortons comparison chart.

The attachment is similar and comes from the updated Dominator Service Notes Chapter 42.

Very usefull, I will get  my printer working  (possibly)   and produce a copy for the workshop wall. Better than relying on data from the worthy  Mr Bacon  who like Haynes did not always get it 100% correct.

Please remember that Mr Bacon was an Author, he spent most of his time rewriting other peoples work. 

My point exactly.

Agreed, as the best advice comes from experience.

Last time I checked my 650 plugs (N4) they were slightly black, probably due to my riding and shorter distances, though starting and general running never an issue.

Having read the above comments, I will change the plugs for new N5's over Easter and monitor before I change the carb settings, which I don't think is an issue. Will let you know.

And thank you all.

I think Its generally accepted that in ideal conditions there should be a light coating of carbon around the mouth of the plug and a very difficult to spot small ring of carbon at the base of the insulator that you can only really inspect by cutting the plug up with an angle grinder . One day sometime maybe never, when i'm truly happy with my running I will do this and post the foto's.