Radar,
I have your 40 Chev in the Gonkulator database as running triple Pinto 2bbl's (the Holley/Weber 5200's). Looks like you swapped intakes? Is the rest of the engine the same ie 228-228 duration cam, headers, etc? With the ported head I had it Gonkulating to about 250hp, in which case it would be happy with 450-500-550cfm on top. A 390cfm should be ok, but what I'm thinking is are the idle transition circuits too small and/or not getting a good signal due to that big cam?
Simple fixes:
1. Turn the idle mix screws OUT as much as you can, not til it slows back down, but get your best idle, then go out another 1/2 turn or so. Maybe more, its easy to try.
2. Make sure the float level is high, gas should dribble out of the sight plug when you take it out.
3. Jet it richer, from the Holley book a #51 comes stock - between our CaliCrap Gas, the cam, and the headers, I'd run at least a #53, maybe #54 main jet.
4. Also make sure you have plenty of initial timing, say 12 degrees, and a fairly quick curve, and that your vacuum advance works. If its not getting enough advance it will complain off the line for sure.
Beyond that the fixes are more complex but I would try those first. Then again its good to have 2 good running carbs anyway so looking for another one wouldn't hurt.
Now and then I sell 4100s but the only one I have ready right now is a 289 HiPo Fairlane carb and its $$$$. I like to get em running first, usually on my 292 six, then make a video of them running & driving. Not a guarantee but a start. But right now I have 3-1bbls on the car so I cant get any carbs ready for a while.
The 4100s aren't too hard to find, if you score one at a swap meet that hasn't been left out in the rain, they usually clean up pretty good. They are so simple you can literally run them with the lid off to check the float levels. And like I said they are pretty re-sellable cuz most of the pre-1967 Fords used em.
Another good pick for that hot 302 would be a 4bbl from a 1970s Ford truck, these were a 550cfm 4bbl, still just about right for your rig. They are good runners, made for a mild 390cid so plenty of idle circuit, and again they are around at swap meets.
