I have a 98 formula z 670 that idles on one cylider. switched carbs still only idles on the same one cylinder. seems to run on both at mid to high rpms. spark is seen on dead cylinder if plug wire is pulled. the cylinder has good compression. both the r.a.v.e. valves are free. is it possible that the rotary timming is off? Just bought it so please respond if you know. Thank You.