Help with compression tester

I just bought this compression tester and it says on carburetor cars to tie a string to the carburetor throttle plates to keep them wide open, but I have fuel injected 5.0 and was wondering if I still have to do this? Also I am testing it without my upper manifold on, so that wouldn't matter anyways, right?? Any help would be great.

thanks for the info. that is reasuring to hear I was hoping I didn't have to do that. I have to take my upper manifold off and install these 24# injectors that is why I asked if I could just test it while it was off.