I've got an auto tranny and mechanical vacuum secondaries. I am curious about this because I have read posts that say vac secondaries work better than mechanical with an auto trans. Can a carb (edelbrock 750) be converted to one from the other? Thanks.

 

Not really. The Edelbrock is a mechanical secondary carb, but the spring loaded secondary air-valve above the throttle plates makes it act somewhat like a vacuum secondary carb.

 

There is a passage drilled on the side of
the carb from the vacuum pot to the primary
and secondary venturi. This senses airflow
thru the venturies {venturi vacuum}. This signal modulates the secondary throttle blades automaticly. It can be adjusted to
suit different cars with the spring in the
vacuum pot.
You cannot convert a double pumper type
carb to vacuum secondaries with out a lot of trouble. Your double pumper can have equal performance by tayloring the accelerator
pump shot timing/vol. Holley has lots of different size pumps : (25cc,30cc 50cc), cams
and shooters available to optimize your setup. But you will need patience and a good selection. Hope this helps....

 

Are we talking about a Holley or an Edelbrock here?

From the original post, I assumed Edelbrock.

If so, you wasted your breath, -Bird...

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. 2-1/2" cat-back, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 CC system w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker 2055 headers, 3" Catco cat & 3" catback, restalled TC, Spohn SFCs).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).