Weber jet recommendation Options

[SKL1]

2.0 with Webcam and Mallory distributor. Timing set and carbs synched, but really flat just off idle. Runs better when further up in the revs.

At 1800' in AZ.

Currently: 40 IDF, 200 air correction, F11 emulsion tube, 115 main, 58 idle, 55 float bowl, 28 venturis

TIA...

[Darren C]

“Darren, have you checked the sync on the carbs? What you're suggesting sounds like a lean overrun, explained like this to me by Racer Chris himself: a lean condition means that ignition does not occur on one compression stroke, then the next time around the excess fuel ignites, causing the overrun (again, only as I understood it). While the 55 idles do sound a little big, you might have one bank, or even one cylinder leaned out too much. Check the sync on both carbs first, with all bypass screws closed. Verify that synch at both idle and at part-throttle. Then move to bringing up the "low" cylinders with the bypass screws. Finally, adjust mixture screws for lean best idle - some folks add an 1/8 turn to make sure they stay a tad bit rich as these engines tend to run best that way (again, just my understanding). If having any issues tuning out the mixture, or if you're more than 2 turns IN, than your idles are too big.”

Many thanks Paintedman, The carbs are balanced with a sync gauge (and to be fair these seem to be the best Webers I’ve ever balanced, they are perfectly matched on all 4 cylinders with the air bleeds shut, all I needed to do was balance them between each carb and the job was done)
I set rough the mixture screws before fitting the carbs by turning in fully closed gently on to the seats, then opening 1 ½ full turns; then ran the engine for the first time to balance up and set idle at about 950 rpm. Checking and rebalancing side to side until perfect. Reving and over run was fine then with no post ignition popping.
It was only when the engine was fully warmed up and I wound the idle screws in to set the mixture by listening to a cylinder drop out (then turning back ¼ turn) when I started to get the popping on over run. Your answer of “lean over run” seems the best explanation. Particularly as I know the mixture screws are more than 2 turns in. (by the way I’ve not heard the 2 turn rule v idle size before) I’ve got some 50 idles, so will swap them over and see how that works out.
Many thanks for the good advice.