Big idle, carbs, checking my work... Options

[VaccaRabite]

Weber 40, IDF carbs. Cable throttle linkage. They are NOT synched yet, and both carbs just had rebuilding work done. I've been working very slow due to time constraints. I fired up the car Friday night!!!

But it was idling at 3000rpm.

After an hour, I had the idle down to 1800 rpm. Both idle adjusters were off the stops. Using a snail, one side was drawing a 7, the other a 14. When I turned off the car, I got a backfire. My "work hour" was done, so I had to leave it at that until the next time I can work - probably next Friday.

So causes for the big idle that I need to investigate:

1. air leaks at base gasket between carb and manifold (reused, very possible)
2. air leaks at top between carb and air filter housing (do they even leak here?)
3. bent butterfly shaft (hope not, and don't think so)
4. slave cable from weak side to strong side needs to be loosened as it is possibly holding throttle open slightly?

Backfire causes:

1. exhaust leak? Fresh installed SSIs, I probably have one at the head somewhere.
2. big carb imbalance? Probably combined with the leak...

Did I miss anything?
Where can I get the good base gaskets? The ones I have are from Weber Carbs Direct and they are the ultra crappy tan cardboard. They took a set and I am sure they are leaking like a sieve.

Zach