So that it's clear - if it turns over, it cranks - think of the days before electric starters were invented - you had to turn the engine over with a hand crank to get them started.
I also want to ask what is your experience level as a mechanic, how familiar are you with carbs, the webers are not the simplest of carbs.
Now, what I can gather from your somewhat confused (and confusing) post is that the engine will only start if you prime the carburettor and it immediately goes to full throttle until the prime is burned off - I believe by "prime" you may be meaning you're filling the float bowl, as no other interpretation of "prime" would allow the engine to run long enough to reach full throttle speeds - this points to a fuel feed problem, either the pump isn't delivering fuel to the carburettor or it's getting to the carburettor but not reaching the float bowl.
For the WOT aspect of things - there can only be one cause - one or both of the throttle plates is open - this would/should have been the first thing you checked when you heard it go full throttle - kill the ignition to prevent the engine over revving and destroying itself - and then check the carb throttle plates.
You have two problem areas which can both be caused by incorrect reassembly or incorrect installation, the fuel feed one can also be caused by a fuel delivery problem (tank/pump/line/filter) so these areas also need to be checked, and be aware that you may need a suitable fuel pressure regulator to run that weber.
Last - I am guessing, from what you have posted, that you do not have that much experience - if I'm right - I suggest you find someone who does to guide you.