[chopper]

mrmike:

FWIW, I've got two 600 cfm vacuum secondary Holley model (P/N 0-1850) on my 484 stroker. The 1850s are sort of the "generic" Holley 600 cfm unit which is used for a number of applications. I removed the chokes completely, have reduced the main jets from the stock #66 to #62. I am planning to reduce further to #60 as it is still running slightly rich, so my personal experience matches Pete Wolff's. I also replaced the vacuum springs with the heaviest ones Holley offers to clear up a bog during acceleration. The car starts with only a couple of pumps of the gas pedal regardless of the temperature. This also worked while I was living in Pennsylvania; during the winter, I would drive the car down to about 40 degrees as long as the roads were clear, and never had a problem starting it. It idles reasonably smoothly at 900 rpm and drives well through the rpm range.

I agree with Darrell in his points. The mechanical secondary versions will give better throttle response assuming the carbs are tuned correctly for the engine. This will entail either some time on a dyno or a bit of "trial and error" tuning to get the appropriate combination of metering jets, power valves and diaphragm springs. Also, the carbs with the metering block (model 4150) will usually not fit on the FE dual-quad manifolds as they are too long.

However, I do have a further question for Darrell or Rob. I understood from one of the Holley reps at a past meet that the 4160 series could not be converted to mechanical secondaries because they lacked a secondary-side accelerator pump. According to him, opening the mechanical secondaries without compensating for the temporary lean condition would result in major bog-down, and that's why Holley didn't sell conversion kits for the linkages. How does the 0-9776 get by with mechanical linkage and no secondary accelerator pump? Inquiring minds want to know.