Vacuum Spring Problem?

well just as an example, here is the formula off Holley's website for sizing. Assuming 100% efficiency, you use this: CID x RPM(where 100% efficiency occurs)/3456

Now, generally, no engine will get to 100% efficient, but you can use you max rpm instead of efficiency rpm. Its not a perfect formula, as most street engines are way below 100% (Holley site says 85%, I tend to think a well tuned street engine will do a little better due to headers, better intakes, ignitions, etc.).
I plugged in the 273, and 6000 rpm, and came out with 474cfm. now normally you'd multiply that by the 85%. according to the site, you need 403CFM. I'd say a more accurate size would be 450.
now here's the kicker...Most Holleys are rated by dry flowing an example of them. Thats the cfm rating you see, like 600, 750, 800, etc. Except, they dont work by moving only air. The fuel in the airstream reduces the total amount of air slightly, so the carbs generally dont flow the rating when on an engine. The Avenger line, and HP lines, are wet flowed, and the cfm ratings are accurate. The same is true for Demon carbs, BG carbs, and every custom carb shop. They all wet flow test.
So, you 600, really flows around 590cfm, but the engine really only needs about 75% of that, and that's assuming you're revving to 6000 rpm. This means you wont be needing the secondaries much to run well with it. As I said, try using the natural spring, and then try the next color stiffer. preferably at the drag strip, so you have a good idea of what it runs. Sorry for the ramble, just thought i'd try to catch the questions before they get asked...lol