[Spridgets] Confused - Weber issues (longish)

[Ron Soave]

I'm having issues with my Weber 45DCOE on a 1275
(street car). The carb is mated to a 3.75" Minispares
manifold, 36mm chokes. The below is a little
convoluted, as things that should have mattered
didn't, so I tried some unconventional things. 

I can't get it to idle properly, it wants to be too
high. I "mixed" it as I usually do - set the idle
speed screw 1/2 turn off the stop, used the mixture
screws to set a smooth running idle, then adjusted RPM
with the idle screw. I can't get the idle below 2200
RPM without backfiring and spitting out the velocity
stacks, even after finding the aux vent screw
replaced. Timing is fine. Valves were fine. No
discernible intake leaks. Replaced points, plugs,
coil, wires, distributor with known good. Definitely
all indications of lean. It runs great once it's off
the progression circuit. So just for grins I upped the
main size from 140 to 160 without changing the air
corrector. It behaves better, I can drop the idle by
500 RPM, but still 500 shy of where I'd like it to be.
The thing is...NONE OF THIS makes sense to me. I
thought the mixture screws set the idle with a small
contribution from the idle jet, and the idle jet
progression circuit takes you from idle to about 2500
RPM, where the main circuit kicks in. **Why did
changing the main jet help at all?** And what will
make it all better completely? When I get back from a
drive, it reeks of gasoline and the plugs look rich. I
only have the idle SPEED screw just barely cracked at
this point, so I don't think I'm doing anything to the
idle progression holes. I have only ever used F9 idle
jets on 4 diffrent Weber setups I've had on my
Sprites, so I don't have any other sizes "in stock". I
tried that little venturi bypass thing, it didn't do
anything.

Any opinions are welcomed. Telling me to switch back
to SUs is obvious so I respectfully ask that you
refrain. I have never had much trouble dialing in a
Weber before.

Ron