Originally Posted by 75gmck25
Also verify the travel on the accelerator cable. I had trouble with my engine flattening out at about 4K RPM and found that I had not adjusted the accelerator cable when I replaced the carburetor. I was not pulling open the secondaries and that is why power went flat.
Good point this happend with one of my porsches. I purchased it from a guy said the motor was bad but the throttle just never opened more than a 1/4 of the way.
Fuel flow can also be effecting the high rpm range if the pump is weak.