How can I tell if my outboards are opening on a six pack?

It is my understanding that the outboard carburetors do not open if you're revving in park in your driveway -- that is to say the engine needs a load placed on it. I remember reading somewhere that people will sometimes place a clip somewhere on the linkage and take the car out, then check the clip for movement.

That sounds like a nice and simple method, are there any other techniques you guys & gals use?

After I get the timing dialed in on this setup, I'm going to look at the outboards because I have a sneaky suspicion they may be hanging up. The throttle shafts are a tad rusty.