I have a new YS 63 and I started test running it today. It is doing the same thing my last YS 63 (the older design) did, it is surging wildly. I hold the throttle steady but the engine revs up and down erratically. I have tried richening/leaning slightly but to no avail. Then the engine just died even though there was fuel in the tank. I hear YSs have problems with surging, what can I do to fix it? Could this be just a normal break-in? Thanks