New plugs new coils still only running half speed. Seems to sputter when throttled all the way. Too much fuel in mix?
Ok, just reviewed everything again. ..you've had many things go wrong. (Prop, shift linkage, low rpm's) did you ever do a compression test? Didn't see one and I'm pretty sure you have over rev'd it many times.
Also, I read you cleaned the carb....but no rebuild? Looks like the gas is not staying atomized.
You have a fuel primer instead of a choke. Read leroysrambilings on how that can cause a rich and or lean situation when it goes bad.
Hopefully you still have good compression.