How does one verify that the secondaries are opening properly on a stock Hitachi 4bbl? The truck seems slower than it should be (but my perception of "fast" is likely mis-calibrated since my daily driver has a Viper V-10 and my other car is an FD).

I tried manually taking the truck to near WOT for a brief second with the truck idling while looking down the carb throat, and I can't seem them opening, but since they're vacuum actuated, I'm not sure that is a valid test.