It was raining here all weekend. This gave me some time to noodle around a little with my car. After some forum research I switched my secondary spring from the long yellow to the white. Test drove her today and It made a noticeable butt dyno improvement. No bog and she will smoke the tires at a higher mph rolling start. I'm no track guy so a little extra tire spin just adds some fun.

 

I have a 4175 Holley 650 CFM vacuum secondary carb for over 30 years and changed to the lightest spring 26 years ago....ran great with the OEM L-82 and same with the rebuilt L-82 355. The heavier springs are really for heavier cars than the C3

 

try the short yellow spring

 

Good job! When folks say a "Holley vacuum sec carb will only allow as much air as the engine needs"....that's not a complete statement.

It will only allow what that spring allows. I've seen engines on the dyno never actually get the secondaries anywhere near wide open. Lighter spring brings it in quicker and allows RPM/airflow to climb and open even more. Similar deal on the air door above the mechanical secondary Q-Jet. If the spring is too tight it will hardly open at all.

Obviously you can go too light...but that's why it's tunable.

JIM

 

Anyone got any pics of this spring.
I've got a spread bore vacume secondary Holley and I can tell they aren't opening all the way. I'm wondering if this will help the problem.
The PO nought the carb and just bolted it on out of th box and didn't tune it at all.

 

watch this video, the spring is inside what the video calls the vacuum unit. I would first check to see if with the engine off, and the gas peddle fully depressed, is the primary side fully opening.

https://www.holley.com/blog/post/4165_4175_carburetors/

 

I recommend the Quick Change Kit. It makes changing springs super easy and fast.

The short yellow is the next up from the white. If I had a bog short yellow would be my go to.

MelWff's video link shows a good pict of the springs at 3.31, The "white" is the far right spring in lineup.