Q Code '72 Convertible carb tuning

[t.kohlmeyer]

Gang:

After many years of fighting the 4300D (715CFM) carb on my Q code, C6 convertible, I finally bagged the carb (literally, I drained and dried it and sealed it in a big freezer ziplock bag), took off the mating iron manifold and wrapped it up in a heavy trash bag.

The engine has a 71 CJ cam (4° advanced from the '72 cam), put in a new set of Crower high rev flat tappets, and buttoned it up with an old D1ZX-9250-DA aluminum (muscle parts) intake. The open chamber heads got new valves, new hardened exhaust seats and bronze guides, plus a cleanup of the ports to remove the casting flaws and blend the valve pockets. I took a die grinder to the factory CJ exhaust manifolds and put on flow master 3 chamber mufflers in the stock 2 1/4" duals. I Topped it off with a Holley
4160 750CFM Vacuum secondary carb,
Part #0-80459SA.

Here's my question: If anyone is running a similar setup, what secondary spring are you using? I've tuned in the idle and checked the float levels, all good. The car runs smoother than the 4300D ever did, but it doesn't seem to pull as hard off idle. I went from the Holley installed black spring to the purple spring. It helped, but just doesn't have the same snap. It would wind up to about 6200 rpm and hard bark both back tires with the 4300D, but now it just barely chirps the tires on the 1-2 shift.

Any input on the way you ended up with your configuration would be appreciated. I'm considering leaning the primaries about 2 sizes and see what happens.

 

[TommyK]

The silver or long yellow spring have always work well for me.

I think the seat of the pants difference you're feeling might have more to do with the intake change than the secondary spring.

Might want to try optimizing the ignition timing for the new combination of parts before getting too deep into the carb.