1977 evinrude 140 hp only 4200 rpms

[evin/skeet]

This motor will only turn 4200 rpm and boat will run 40mph at wot. The engine plate says it should turn 4500 - 5500rpm and 140hp @5000rpm. At first it had a 21 pich prop and i was told it was probably just a prop issue so i put a 19 pich on, no change in rpm so i went down to 17 pich prop no change in rpm still, so i went down to a 15 pich prop still no change in rpms. All four cylinders have around 120# compression. the motor is on a jack plate(not hydrolic) and set where the skeg is level with bottom of hull, i have moved it up and down and has little or no effect. I have been told the rev limiter is the issue also been told the stator and or timer base could be bad. The tachometer is set on four cylinder and reads 1000 rpm at idle, the motor is a little cold natured it will fire right up and idle a second or two and abruptly stop and sounds like it is relieving compression when it does like a quick hiss noise but if you keep your foot in the gas just a little for a minute until it warms up it does fine once it is hot. My main question is why will this motor only turn 4200rpms.