I thought I saw a pic somewhere else where you had your PCV hooked into the intake and brake booster into the carb. Reverse that.
Don't bother with the closed PCV line between the valve cover and the air filter. Use a filter on the valve cover. The PCV should pull vacuum from the carb to the cover. The filter is to allow air in. If it's going the other way something is wrong (bad PCV valve? Cheap...)
Your times are doggedly slow. My 1bbl, stock set up was faster than that. You should be MUCH faster with a 4bbl.
Check for vacuum leaks. Start by pinching hoses with the car running. If you notice a difference in RPM you found your leak.
There are 3 vacuum connections on the carb. The big one goes to the PCV valve. The top one goes to the vac advance. The bottom one goes to the trans (if needed. If not needed plug it).
Is the intake manifold sealing properly? Spray carb cleaner at the mating surfaces to find out.
Hesitation: Adjust your accelerator pump cam. It should be set so when the throttle is wide open the arm is almost fully compressing the plunger.
Is your electric choke working properly? Staying connected?
Check float level.
Somethings I had that screwed with me:
1) The vac line to the trans was bad at the trans. There's a hard line that runs down to the top of the output shaft on the powerglide and ends with a short rubber hose and into the trans. That hose was toast.
2) The accellerator pump BB is held in place with a brass bar. That bar fell out and the BB was rolling around in the rubber plunger. I found that one with pure luck. Put it back in, used a punch to stamp the ends of the bar to secure it and put it all back together. Magic happened.
3) Secondary spring: Put in the second to the lightest one. That'll open the secondaries a bit sooner and help that time. They don't tend to open very soon with the 250's. Not enough air flowing through to draw it open.
4) Had a bad float. Well the float was OK but the back arm was broken. Couldn't find it until I removed the float and found this:
My set up: Offy intake, Holley 390, Langdon headers, 2.5" single exhaust, HEI.
Initial timing at 12, 30+ all in (don't recall)
Primary jets: 54
Squirter: 28
Secondary spring: Second to the lightest
Pics if it'll help:
(I've changed stuff since then but this'll get you in the right direction)
Duece said you don't need HEI yet but I beg to differ. If your distributor is worn you might as well do it.
http://www.ebay.com/itm/CHEVY-INLINE-6-C...fb5&vxp=mtr$60. Cheap and works well. The vac advance is adjustable with this one. You use an allen wrench in the vac line hole in the canister and you can change it. I played with mine to get it right. Don't recall the settings. Regardless going this route made a HUGE difference in how mine idles. Smoothed it out a lot.
After all that I also had to go to mid grade gas to keep from pinging.
