I have a 1987 200 yamaha that came on a boat I just purchased. The problem is no power. It won't go over 1400 rpm. I have changed the anti-siphon valve,drained the fuel tank, new fuel line from the tank on, new fuel filters,new fuel pumps, new spark plug boots,new plugs,and rebuilt carbs. I also bypassed the filters, primer bulb and motor connector. It starts OK and idles well. Tried the choke at open throttle and it wanted to die. I checked the spark and it seemed OK(jumped a 1/4" gap)except for all cylinders it cut out for about 3 or 4 seconds then would resume. Tried to disconnect the ground to the control unit to see if that would help and no joy.Any suggestions?