WE’VE GOT MAIL!

Some really entertaining letters here. It’s impossible to receive too many letters. We want more letters. Be kind to us…

Just read Members’ Enclosure with RC184 about spark plugs. I have been an NGK kinda guy for almost all my motorcycling days. However, recently I have fitted Brisk spark plugs (available from David Angel at F2) and these have improved the starting on both my CZs. It also improved fuel consumption, with my Custom managing 50 miles on 2.5 litres one day and 87 miles on 5 litres on another.

The man with the Arrow might improve his Ariel by fitting Brisk spark plugs; I’m sure David at F2 would be able to advise and supply these alternatives. They are better fitted without resistor plug caps. As a twostroke person myself, I would always try Brisk now instead of NGK. My loyalties have been swayed by the easier starting and sweeter running of a two-stroke engine!

Andrew L Smith, member 4609

Having suffered a number of spark-plug related roadside failures on my Matchless G5 over the years, I was very interested to read why this may happen. I know this is probably tempting fate, but I’ve so far not had a spark plug failure issue after switching from modern plugs to vintage NOS equivalents. My theory on why this has worked successfully for me and why modern plugs fail in classic motorcycles has two main reasons:

Modern internal combustion engines are designed to run with accurately metered fuel injection to meet environmental emission legislation. As a consequence plugs don’t foul, so for cost saving reasons many spark plug manufacturers today no longer glaze the centre electrode porcelain insulator

Modern fuels contain a range of additives that can accumulate in and around the centre electrode porcelain. If not fully burned off by the combustion process they are gradually absorbed by the unglazed porcelain, reducing its insulation properties eventually providing a conductive path to the plug’s metal body

Nowadays I only use spark plugs manufactured up to the early 1970s, safe in the knowledge that these vintage plugs are more compatible with my classic bike and tolerant with the short-ish journeys that I make on it.

Many thanks for producing for what I think is by far the best classic bike publication and every month I look forward to it hitting my doormat! Chris Tovey, member

I did say it was complicated, didn’t I? Thanks everyone for the observations and suggestions. Now remember, if it’s not the spark plug then it’s almost certainly the carb… Rowena