Odd miss on the left side

[apull]

I appreciate the help given with my battery problems and now I am looking for ideas about my next problem.  Background: I bought the bike new in 79 and very shortly after warranty was out a 851 Vinola (sp) kit was added.  The bike has about 60,000 miles (shows 20000 on 3rd odometer repair)  I am 78 and the bike doesn't get ridden very much anymore.  The motor fires up and starts running on the right side now I can start to remove the left plug wire and  before it comes off, just barely on, the left cylinder starts to fire.  If I push the plug wire back on it starts to miss. Plugs are BERU Z42  14-5DU gap .029. Wires are NGK and fairly new. Any ideas??  and thanks for this site.  

[Barry]

Pulling off the plug cap is creating a gap for the spark to jump across which forces the ignition system to create a higher voltage and that is enough to overcome whatever is wrong with the spark plug hence the left side starts to fire cleanly. Some plugs used to have such a spark gap built in for the same purpose.  I'd try cleaning/replacing the plug.

The Beru plug sounds correct as they use the same heat range coding system as Bosch so they would be the equivalent of Bosch W5DC

[apull]

Thanks,  What plugs are others using in the older R65's?

[Barry]

Many people use the NGK BP7ES which is considered one of the very best plugs, I use the Denso W22EP-U which I think is just as good. Both of these are non resistor plugs which is desirable especially with points ignition. Bosch W5DC was the originally specified plug but they are not easily found now as a none resistor type.