[My427stang]

1. Set the timing to 12 initial, even 15 if it'll start when hot, but 8 IMHO is way too low for a light car.
2. Set the idle speed and then see if you have vacuum at the fitting off the metering block (if you do, your primary plates are too far open and you are out of the idle circuit, I'll bet bucks you are)

3. Assuming you are, pull the carb off and from the bottom back right under the vac canister, open the secondaries about 60 thousands or so using a little screwdriver on the secondary idle adjustment, just guesstimate, turn it in tighter 1 1/2 or two turns, but basically you are opening the back so you can close the front. Dont worry about how much, just open them a little. Holleys always use a secondary idle circuit as well, to keep fuel from going stale in the back bowls, you are just going to use it a bit more so you can close the fronts and be able to clean up the idle

4. Put the carb back on, it'll be idling high now, drop the primary idle down, adjust the a/f again and see if that port is alive again, if it is, add a little more secondary idle again and do the same thing

5. After you get it to where the ported vacuum is dead at idle (no vacuum at all) if it is still rich, you may have to swap plates in the back. You have a 21 plate which is jetted properly for yours, but the Idle Feed Restriction is a .059 i beleive on factory 3310's, if you go for a plate number 44, it will lean out the idle with the same main jet size BUT the part that will ehlp is that the IFR is .029

The last thing I have seen is that the 3310-4 has a 25 squirter, most others have a 31. The FE seems to like the 25 so the shot last longer. I actually changed my 850 from dual 35's and a 50cc pump to dual 25's and 30cc pumps. If you have anyhting other than a 3310-4 change the squirter to a 25

I bet the first part adjusting the idle to take more from the back will give you the 90% solution, chase the others if you need it