Quote:
Originally Posted by Luke427
While I could agree with the last statements, there's been some interesting findings there - secondaries not behaving correctly resulting in terrible engine response, dangerous for regular drivers and uncomfortable for advanced drivers.
Jumping from 20% to 100% throttle over half an inch pedal throttle and 500 RPM isn't what one should expect, especially with 560 hp  |
That definitely is not how Holley vacuum secondary 4 bbl carbs are designed to operate. Although it's commonly stated that vacuum instantly drops to zero when the throttle is matted (usually when talking about vacuum advance), that's not accurate as far as what the carb is seeing internally. There is residual vacuum depending on engine size, rpm, load and carb size. The residual vacuum (my term - not sure what carb designers call it) will fall gradually as engine load and rpm catch up to the primary air flow capacity and as determined by the vacuum secondary spring, the rear throttle plates will then begin to open. From that point on it's a balancing act as the demand for more air keeps pulling vacuum lower and lower and pulling the secondaries further open against the spring pressure.
The mechanical linkage sounds typical - not actually sure if it's primary purpose is to prevent early opening of the secondaries, to ensure closing of the secondaries on lifting off the throttle or both. I would pull the carbs, get a good Holley book at the book store and see what you have inside the vacuum secondary pods. Possibly a check valve ball is missing in them or something. Or, could just need a heavier spring to slow their opening down.