My GN 250 has a problem with the rpm. At times its unstable either dropping and cutting off the engine or rising by 2-4000 rpm without throttle or idle screw adjustment. My base RPM on idle is 1500-2000, i can get it to stabilise for a time by minor idle screw increments but any throttle rises and stays on the rpm and i have to loosen the idle screw to drop it again. Because of this problem i have not taken it on road but even when its moving the rpm drops. Any help would be great, thanks