RE: evolution 61nx
You may see better rpms and less fuel being spit out the exhaust by using an OS A3 plug. I think the whole Evolution line of 2 strokes suffer from running too cold with plugs in the normal heat range. A hot plug will burn the excess fuel that the colder plug won't. More power and less fuel needed. Better acceleration. Better starting.
How do you tune the engine? Have you adjusted the low speed needle?