OK well here's where I'd start;
First a few caveats;
1) If your cam is bigger than 292/292/108, I'm not your guy, wait for somebody smarter than me to show up.
2) If your distributor is locked at any particular timing and/or the distributor does Not have a VA system, I cannot help you.
3) If your cam Is smaller than or equal to, that 292, I have tuned a few of of those. and others down to 262s. I'll try to help you.
4) if you have the PCV system plumbed to #5 intake runner, that's bad. Put it where it belongs, entering the carb just under the Primary blades near the discharge ports. I leave it on you, to prove that the PCV is working and that all the other air that the engine is getting, is coming in past the throttles.
5) If you have power brakes, they gotta be plumbed to the port on the BACK of the carb, or to a spacer under the carb, or to the plenum, but NOT, to any single runner; and of course, that line better not be sucking air full-time.
BTW-1
Isn't that Xcellerator a small-port, small-plenum intake? What cam is in that beast?
I tried that Intake on my 367 with a 292 cam; Why?, because I had it. no bueno. I installed the AirGap; mucho bueno.
Ok here we go. As to, What I would do;
I'd take the carb off, drain it, flip it upside down making sure the throttle is on the curb idle screw then LOOK at the Transfer Slot exposure on the underside of the Primary blades. Make a note of how far the slots are showing, for future reference.
A) If they are not at least square with a 4-corner idle then make them so.
B) If you do NOT have a 4-corner idle, then make them noticeably taller than square. then, slam the secondaries shut.
Then set the mixture screws to in the middle of their range.
Finally, bolt the carb back on, fill it thru the bowl-vents, reset your accelerator pumps, and your throttle slack; as may be required.
Start it up and while it's warming up; make sure the fuel level is correct and stable, but
DO NOT TOUCH THE CURB IDLE SCREW.
After it is warmed up, change your idle speed using Ignition timing, to whatever you think is appropriate for your cam/combo. Then diddle the mixture screws for best Idle.
If the engine likes a lil more, or a lil less gas at idle than what the mixture screws can give while set to say 1/2 turn from in the middle of their range, add or subtract a 1/2 turn Curb-idle, and Put the screws back! If the idle-speed changes, reset it with timing. Repeat until yur happy but
a) do not let the slot exposure go to less than square, and/or
b) nor the timing to less than 12*.
The reason is that doing so will usually introduce an incurable off-idle stumble, as the slots progressively shut down.
Now check that cylinder again.
If this works;
You will have to re-engineer all your other timings; like Power-Timing and Stall-Timing and Cruize-Timing and Part-Throttle Timing. But for crying out loud, leave the Curb-Idle screw alone.
If this doesn't work,
maybe you got 7 other lobes going flat. lol.
If you have a 4-corner idle, you may have to introduce air AND/OR fuel, into the Secondaries. If you add both, the idlespeed may/will go up. If the timing is already down to 14 or less, this may be a problem . Most likely you will have to shut the secondaries off and introduce Idle-Air bypass into the Primaries.
I think that small-plenum Weiand does not like dry air coming in thru the Secondaries. For me, two of the back four cylinders went lean.
And, I have never had success tuning a big cam at idle with an AFR gauge. Your results may vary.
Ok I'm all done;
Happy Hotrodding.