Mercury 175 no mid-range

[champion21]

~~I own a 1987 Mercury Black Max 175HP serial number 0B143571. My problem is the motor starts and idles fine, but in the water when I put it in gear it will run great up to about 1200 rpm’s, after that it dies. But if I jam the throttle all the way forward it takes off, and after it planes out it will do every bit of 65 mph all day long. If I drop the throttle back the engine dies unless I drop it all the way back to idle. In other words it has a dead spot. So far I have rebuilt the carburetors, used Sea Foam in the gas, rebuilt the oil pump, rebuilt the fuel pump, checked compression and all cylinders are equal at 90 psi, changed the spark plugs with new, set the timing and synchronized, removed the fly wheel and checked the stator and trigger, I have downloaded CDI’s trouble shooting guide, disconnected the idle advance box, rebuilt the water pump, and disconnected the spark plugs one at a time and all working fine. When I had the flywheel off I disconnected the wires from the switch boxes and checked the resistances. From the blue/blue white wires I had 3200 and 4200 ohms, on the red/red white wires both were 68 ohms. the trigger was good on all checks. When running I checked the DVA on the green wires to the coils. On #6 I had 125 volts, #4 I had 110 volts and #2 I had 100 volts. Can anyone help?