YamTDR250

Hello all! I've had my H reg TDR250 from new and has only covered 5700mls(i know it's a waste). I've now got a problem with the ignition! It starts fine on choke and will tick over but if i rev it(about 6000revs) up it seems to cut out and can see this on the rev counter as the needle drops straight down and once the rev drop abit the needle kick back up when the engine starts firing again. I've changed the coil and this has not cured it. I would be greatfull for any help as i'm now just scratching my head