Just replaced the plug on my mk 1 with an NGK B9EGV. A few days later bike sputtered to a halt on way home from work. After playing around a mechanic friend replaced the plug with another B9EGV and bike started first kick. He left and 15 minutes later the bike sputters to a halt and won't restart again. Obviously suspect that the plug is shot again but why are my plugs only lasting 15 minutes?
any help appreciated.

Try an 'R'plug the R means resistor=BR*****.
Bad coil earth,bad coil

throwing a B9EVG won't do anything to any other part than your indicator relay (blows the fuse) go to your nearest honda shop and get yourself an NGK spark plug resistor plug to solve the problem.

Put a BR8ES plug in last week and all seems fine so far. Still Cant work out why the b9's dont work. The cap has a 5K resistance, and as i understand it the resistance is there to stop interference with electronic gadgets so not a problem on a crm.But as she runs fine on br8's i'll stick with them.

Leisure and trail advised that the B8EVG was the one to go for if I am not racing. I ride green lanes so seldom get to full throttle
So far so good easy to restart when hot or cold. 8)