Well, start by dialing that timing back a bit...just from my rough calculations...you have a comp ratio over 9.25:1. Set it for about 30-32 ALL IN by 3000. Get it warm, and set the valve lash...then go back to tuning...I would reccomend you buy a good weber tuning book...the Speedpro series is one "How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburettors"
As far as the carbs closing, you have to run an external return spring...there is no other way around it....Consider it a requirement....both by the DOT, and the SCCA. EVERY application I have seen for DCOE style carbs, both Factory OEM and Aftermarket, used some sort of return spring on the throttle linkage or the shaft.
Also, look into changing out the Idle jets to a 50f9...you will have to try out a few different jets...nut the f11 series idles have far too much emulsification for our cars...other than that...your jetting looks ok for starters. Where are you located, and are you getting oxygenated fuels...that can make a HUGE difference in jetting