14-06-16, 06:08 PM
It'll just sound a bit noisy running on three with a plug out, there's not much going on in the cylinder as there's no vacuum to draw air and fuel in with the plug out. I think yamaha say the spark should jump a minimum of 6mm when the ignition system is healthy. I've had problems with my plug caps, a few forum members have told me the NGK caps work perfectly well. The originals are bloody expensive.
Rust never sleeps !